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Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John Hock [email protected] Dan Braden [email protected] Power Systems Advanced Technical Skills
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Page 1: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3

Path Management and SAN Boot with MPIO on AIX

John Hock [email protected] Braden [email protected]

Power Systems Advanced Technical Skills

Page 2: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

2 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Agenda

Correctly Configuring Your Disks► Filesets for disks and multipath code

Multi-path basics Multi Path I/O (MPIO)

►Useful MPIO Commands

►Path priorities

►Failed Path Recovery and path health checking

►MPIO path management SDD and SDDPCM Multi-path code choices for DS4000, DS5000

and DS3950 XIV & Nseries SAN Boot

Page 3: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

3 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Disk configuration

The disk vendor… Dictates what multi-path code can be used Supplies the filesets for the disks and multipath code Supports the components that they supply

A fileset is loaded to update the ODM to support the storage AIX then recognizes and appropriately configures the disk Without this, disks are configured using a generic ODM definition

Performance and error handling may suffer as a result # lsdev –Pc disk displays supported storage

The multi-path code will be a different fileset Unless using the MPIO that’s included with AIX

Beware of generic “Other” disk definition

No command queuing. Poor Performance & Error Handling

https://tuf.hds.com/gsc/bin/view/Main/AIXODMUpdates 

ftp://ftp.emc.com/pub/elab/aix/ODM_DEFINITIONS/

Page 4: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

4 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

How many paths for a LUN?

Server

FC Switch

Storage

• Paths = (# of paths from server to switch) x (# paths from storage to switch)…Here there are potentially 6 paths per LUN

…But reduced via:• LUN masking at the storage

Assign LUNs to specific FC adapters at the host, and thru specific ports on the storage

• ZoningWWPN or SAN switch port zoning

• Dual SAN fabricsdivides potential paths by two

• 4 paths per LUN are sufficient for availability and reduces CPU overhead for choosing the path• Path selection overhead is relatively low—usually negligible

• MPIO has no practical limits to number of paths• Other products have path limits

• SDDPCM limited to 32 paths per LUN

Page 5: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

5 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

How many paths for a LUN?, cont’dDual SAN Fabric Reduces Potential Paths

4 X 4 = 16

Server

FC Switch

Storage

2 X 2 + 2 X 2 = 8

Page 6: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

6 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Path selection algorithms choose a path to hopefully minimize latency added to an IO to send it over the SAN to the storage Latency to send a 4 KB IO over a 8 Gbps SAN link is 4 KB / (8 Gb/s x 0.1 B/b x1048576 KB/GB) = 0.0048 ms

Multiple links may be involved, and IOs are round trip As compared to fastest IO service times around 1 ms

If the links aren’t busy, there likely won’t be much, if any, savings from use of sophisticated path selection algorithims vs. round robin

Costs of path selection algorithms CPU cycles to choose the best path Memory to keep track of in-flight IOs down each path, or Memory to keep track of IO service times down each path Latency added to the IO to choose the best path

Path selection algorithms choose a path to hopefully minimize latency added to an IO to send it over the SAN to the storage Latency to send a 4 KB IO over a 8 Gbps SAN link is 4 KB / (8 Gb/s x 0.1 B/b x1048576 KB/GB) = 0.0048 ms

Multiple links may be involved, and IOs are round trip As compared to fastest IO service times around 1 ms

If the links aren’t busy, there likely won’t be much, if any, savings from use of sophisticated path selection algorithims vs. round robin

Costs of path selection algorithms CPU cycles to choose the best path Memory to keep track of in-flight IOs down each path, or Memory to keep track of IO service times down each path Latency added to the IO to choose the best path

Path selection benefits and costs

Generally utilizationof links is low

Page 7: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

7 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Multi-path IO with VIO and VSCSI LUNs

VIO ClientMPIO

VIO ServerMulti-path code

VIO ServerMulti-path code

Disk Subsystem

Two layers of multi-path code: VIOC and VIOS

VSCSI disks always use AIX default MPIO and all IO for a LUN normally goes to one VIOS

► algorithm = fail_over only

VIOS uses the multi-path code specified for the disk subsystem

Set the path priorities for the VSCSI hdisks so half use one VIOS, and half use the other

Page 8: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

8 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Multi-path IO with VIO and NPIV

VIO ClientMulti-path code

VIO Server VIO Server

Disk Subsystem

VIOC has virtual FC adapters (vFC)► Potentially one vFC adapter for every real FC adapter

in each VIOC

► Maximum of 64 vFC adapters per real FC adapter recommended

VIOC uses multi-path code that the disk subsystem supports

IOs for a LUN can go thru both VIOSs

One layer of multi-path code

VFC VFC VFC VFC

Page 9: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

9 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

What is MPIO?

MPIO is an architecture designed by AIX development (released in AIX V5.2) MPIO is also a commonly used acronym for Multi-Path IO

► In this presentation MPIO refers explicitly to the architecture, not the acronym

Why was the MPIO architecture developed?► With the advent of SANs, each disk subsystem vendor wrote their own multi-path code

► These multi-path code sets were usually incompatible

● Mixing disk subsystems was usually not supported on the same system, and if they were, they usually required their own FC adapters

► Integration with AIX IO error handling and recovery

● Several levels of IO timeouts: basic IO timeout, FC path timeout, etc

MPIO architecture details available to disk subsystem vendors► Compliant code requires a Path Control Module (PCM) for each disk subsystem

► Default PCMs for SCSI and FC exist on AIX and often used by the vendors

► Capabilities exist for different path selection algorithms

► Disk vendors have been moving towards MPIO compliant code

MPIO Common Interface

Page 10: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

10 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Overview of MPIO Architecture

LUNs show up as an hdisk►Architected for 32 K paths

►No more than 16 paths are necessary PCM: Path Control Module

►Default PCMs exist for FC, SCSI

►Vendors may write optional PCMs

►May provide commands to manage paths Allows various algorithms to balance use

of paths Full support for multiple paths to rootvg

Hdisks can be Available, Defined or non-existent Paths can also be Available, Defined, Missing or non-existent Path status can be enabled, disabled or failed if the path is Available

(use chpath command to change status) Add path: e.g. after installing new adapter and cable to the disk

run cfgmgr (or cfgmgr –l <adapter>) One must get the device layer correct, before working with the path status layer

Hdisks can be Available, Defined or non-existent Paths can also be Available, Defined, Missing or non-existent Path status can be enabled, disabled or failed if the path is Available

(use chpath command to change status) Add path: e.g. after installing new adapter and cable to the disk

run cfgmgr (or cfgmgr –l <adapter>) One must get the device layer correct, before working with the path status layer

Tip: to keep paths <= 16, groupsets of 4 host ports and 4 storage ports and balance LUNs across them

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11 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

MPIO support

Storage Subsystem Family MPIO code Multi-path algorithm

IBM ESS, DS6000, DS8000, DS3950, DS4000, DS5000,

SVC, V7000

IBM Subsystem Device Driver Path Control Module (SDDPCM)

fail_over, round_robin, load balance, load balance port

DS3/4/5000 in VIOSDefault FC PCM recommended

fail_over, round_robin

IBM XIV Storage System Default FC PCM fail_over, round_robin

IBM System Storage N Series Default FC PCM fail_over, round_robin

EMC Symmetrix Default FC PCM fail_over, round_robin

HP & HDS(varies by model)

Hitachi Dynamic Link Manager (HDLM)

fail_over, round robin, extended round robin

Default FC PCM fail_over, round_robin

SCSI Default SCSI PCM fail_over, round_robin

VIO VSCSI Default SCSI PCM fail_over

Page 12: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

12 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Non-MPIO multi-path code

Storage subsystem family Multi-path code

IBM DS4000 Redundant Disk Array Controller (RDAC)

EMC Power Path

HP AutoPath

HDS HDLM (older versions)

Vertias supported storage Dynamic MultiPathing (DMP)

Page 13: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

13 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Mixing multi-path code sets

The disk subsystem vendor specifies what multi-path code is supported for their storage

►The disk subsystem vendor supports their storage, the server vendor generally doesn’t

You can mix multi-path code compliant with MPIO and even share adapters

►There may be exceptions. Contact vendor for latest updates.

HP example: “Connection to a common server with different HBAs requires separate HBA

zones for XP, VA, and EVA”

Generally one non-MPIO compliant code set can exist with other MPIO compliant code sets

►Except that SDD and RDAC can be mixed on the same LPAR

►The non-MPIO compliant code must be using its own adapters

Devices of a given type use only one multi-path code set

►e.g., you can’t used SDDPCM for one DS8000 and SDD for another DS8000 on the same

AIX instance

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14 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Sharing Fibre Channel Adapter ports

Disk using MPIO compliant code sets can share adapter ports

It’s recommended that disk and tape use separate ports

Disk (typicaly small block random) and tape (typically large block sequential) IO are different, and stability issues have

been seen at high IO rates 

Page 15: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

15 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

MPIO Command Set

lspath – list paths, path status and path attributes for a disk

chpath – change path status or path attributes►Enable or disable paths

rmpath – delete or change path state ►Putting a path into the defined mode means it won’t be used (from available to

defined)

►One cannot define/delete the last path of a device

mkpath – add another path to a device or makes a defined path available ►Generally cfgmgr is used to add new paths

chdev – change a device’s attributes (not specific to MPIO)

cfgmgr – add new paths to an hdisk or make defined paths available (not specific to MPIO)

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16 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Useful MPIO Commands

List status of the paths and the parent device (or adapter)

# lspath -Hl <hdisk#> List connection information for a path

# lspath -l hdisk2 -F"status parent connection path_status path_id“Enabled fscsi0 203900a0b8478dda,f000000000000 Available 0Enabled fscsi0 201800a0b8478dda,f000000000000 Available 1Enabled fscsi1 201900a0b8478dda,f000000000000 Available 2Enabled fscsi1 203800a0b8478dda,f000000000000 Available 3

The connection field contains the storage port WWPN► In the case above, paths go to two storage ports and WWPNs:

203900a0b8478dda201800a0b8478dda

List a specific path's attributes

# lspath -AEl hdisk2 -p fscsi0 –w “203900a0b8478dda,f00000000000“scsi_id 0x30400 SCSI ID Falsenode_name 0x200800a0b8478dda FC Node Name Falsepriority 1 Priority True

Page 17: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

17 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Path priorities

A Priority Attribute for paths can be used to specify a preference for path IOs. How it works depends whether the hdisk’s algorithm attribute is set to fail_over or round_robin.

Value specified is inverse to priority, i.e. “1” is high priority

algorithm=fail_over►the path with the higher priority value handles all the IOs unless there's a path failure.

►the other path(s) will only be used when there is a path failure.

►Set the primary path to be used by setting it's priority value to 1, and the next path's priority (in case of path failure) to 2, and so on.

►if the path priorities are the same and algorithm=fail_over, the primary path will be the first listed for the hdisk in the CuPath ODM as shown by # odmget CuPath

algorithm=round_robin►If the priority attributes are the same, then IOs go down each path equally.

►In the case of two paths, if you set path A’s priority to 1 and path B’s to 255, then for every IO going down path A, there will be 255 IOs sent down path B.

To change the path priority of an MPIO device on a VIO client:# chpath -l hdisk0 -p vscsi1 -a priority=2

►Set path priorities for VSCSI disks to balance use of VIOSs 

Page 18: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

18 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Path priorities

# lsattr -El hdisk9PCM PCM/friend/otherapdisk Path Control Module Falsealgorithm fail_over Algorithm Truehcheck_interval 60 Health Check Interval Truehcheck_mode nonactive Health Check Mode Truelun_id 0x5000000000000 Logical Unit Number ID Falsenode_name 0x20060080e517b6ba FC Node Name Falsequeue_depth 10 Queue DEPTH Truereserve_policy single_path Reserve Policy Trueww_name 0x20160080e517b6ba FC World Wide Name False…

# lspath -l hdisk9 -F"parent connection status path_status"fscsi1 20160080e517b6ba,5000000000000 Enabled Availablefscsi1 20170080e517b6ba,5000000000000 Enabled Available

# lspath -AEl hdisk9 -p fscsi1 -w"20160080e517b6ba,5000000000000"scsi_id 0x10a00 SCSI ID Falsenode_name 0x20060080e517b6ba FC Node Name Falsepriority 1 Priority True

Note: whether or not path priorities apply depends on the PCM. With SDDPCM, path priorities only apply when the algorithm used is fail over (fo). Otherwise, they aren’t used.

Note: whether or not path priorities apply depends on the PCM. With SDDPCM, path priorities only apply when the algorithm used is fail over (fo). Otherwise, they aren’t used.

Page 19: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

19 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Path priorities – why change them?

With VIOCs, send the IOs for half the LUNs to one VIOS and half to the other

►Set priorities for half the LUNs to use VIOSa/vscsi0 and half to use VIOSb/vscsi1

►Uses both VIOSs CPU and virtual adapters

►algorithm=fail_over is the only option at the VIOC for VSCSI disks

With NSeries – have the IOs go the primary controller for the LUN►Set via the dotpaths utility that comes with Nseries filesets

Page 20: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

20 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Path Health Checking and Recovery

Validate a path is working Automate recovery of path

For SDDPCM and MPIO compliant disks, two hdisk attributes apply:

# lsattr -El hdisk26 hcheck_interval 0 Health Check Interval Truehcheck_mode nonactive Health Check Mode True

hcheck_interval ► Defines how often the health check is performed on the paths for a device. The attribute supports a

range from 0 to 3600 seconds. When a value of 0 is selected (the default), health checking is disabled► Preferably set to at least 2X IO timeout value

hcheck_mode► Determines which paths should be checked when the health check capability is used:

● enabled: Sends the healthcheck command down paths with a state of enabled ● failed: Sends the healthcheck command down paths with a state of failed● nonactive: (Default) Sends the healthcheck command down paths that have no active I/O, including

paths with a state of failed. If the algorithm selected is failover, then the healthcheck command is also sent on each of the paths that have a state of enabled but have no active IO. If the algorithm selected is round_robin, then the healthcheck command is only sent on paths with a state of failed, because the round_robin algorithm keeps all enabled paths active with IO.

Consider setting up error notification for path failures (later slide)

Page 21: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

21 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Path Recovery MPIO will recover failed paths if path health checking is enabled with hcheck_mode=nonactive or failed

and the device has been opened

Trade-offs exist:► Lots of path health checking can create a lot of SAN traffic

► Automatic recovery requires turning on path health checking for each LUN

► Lots of time between health checks means paths will take longer to recover after repair

► Health checking for a single LUN is often sufficient to monitor all the physical paths, but not to recover them

SDD and SDDPCM also recover failed paths automatically

In addition, SDDPCM provides a health check daemon to provide an automated method of reclaiming failed paths to a closed device.

To manually enable a failed path after repair or re-enable a disabled path: # chpath -l hdisk1 -p <parent> –w <connection> -s enable

To disable all paths using a specific FC port on the host:

# chpath –l hdisk1 –p <parent> -s disable

Page 22: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

22 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Path Health Checking and Recovery – Notification!

One should also set up error notification for path failure, so that someone knows about it and can correct it before something else fails.

This is accomplished by determining the error that shows up in the error log when a path fails (via testing), and then

Adding an entry to the errnotify ODM class for that error which calls a script (that you write) that notifies someone that a path has failed.

Hint: You can use # odmget errnotify to see what the entries (or stanzas) look like, then you create a stanza and use the odmadd command to add it to the errnotify class.

Page 23: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

23 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Path management with MPIO Includes examining, adding, removing, enabling and disabling paths

► Adapter failure/replacement or addition

► VIOS upgrades (VIOS or multi-path code)

► Cable failure and replacement

► Storage controller/port failure and repair Adapter replacement

► Paths will not be in use if the adapter has failed, paths will be in the failed state

1. Remove paths with # rmpath –l <hdisk> -p <parent> -w <connection> [-d]-d will remove the path, without it the path will changed to Defined

2. Remove the adapter with # rmdev –Rdl <fcs#>

3. Replace the adapter

4. cfgmgr

5. Check the paths with lspath It’s better to stop using a path before you know the path will disappear

► Avoid timeouts, application delays or performance impacts and potential error recovery bugs

Page 24: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

24 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Active/Active vs. Active/Passive Disk Subsystem Controllers

IOs for a LUN can be sent to any storage port with Active/Active controllers

LUNs are balanced across controllers for Active/Passive disk subsystems

► So a controller is active for some LUNs, but passive for the others

IOs for a LUN are only sent to the Active controller’s port for disk subsystems with Active/Passive controllers

► ESS, DS6000, DS8000, and XIV have active/active controllers

► DS4000, DS5000, DS3950, Nseries, V7000 have active/passive controllers

● The NSeries passive controller can accept IOs but IO latency is affected► The passive controller takes over in the event the active controller or all paths to it fail

MPIO recognizes Active/Passive disk subsystems and sends IOs only to the primary controller

► Except under failure conditions, then the active/passive role switches for the affected LUNs

Terminology regaring active/active and active/passive varies considerably

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25 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Example: Active/Passive Paths

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26 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

SDD: An Overview

SDD = Subsystem Device Driver – Pre-MPIO Architecture

Used with IBM ESS, DS6000, DS8000 and the SAN Volume Controller, but is not MPIO compliant

►A “host attachment” fileset (provides subsystem-specific support code & populates the ODM) and SDD fileset are both installed

►Host attachment: ibm2105.rte

►SDD: devices.sdd.<sdd_version>.rte

LUNs show up as vpaths, with an hdisk device for each path►32 paths maximum per LUN, but less are recommended with more than 600 LUNs

One installs SDDPCM or SDD, not both.

No support for rootvg, dump or paging devices► One can exclude disks from SDD control using the excludesddcfg command

► Mirror rootvg across two separate LUNs on different adapters for availability

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27 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

SDD

Load balancing algorithms ►fo: failover

►rr: round robin

►lb: load balancing (aka. df or the default) and chooses adapter with fewest in-flight IOs

►lbs: load balancing sequential – optimized for sequential IO

►rrs: round robin sequential – optimized for sequential IO

The datapath command is used to examine vpaths, adapters, paths, vpath statistics, path statistics, adapter statistics, dynamically change the load balancing algorithm, and other administrative tasks such as adapter replacement, disabling paths, etc.

mkvg4vp is used instead of mkvg, and extendvg4vp is used instead of extendvg

SDD automatically recovers failed paths that have been repaired via the sddsrv daemon

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28 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Does Load Balancing Improve Performance?

Load balancing tried to reduce latency by picking a less active path ► …but adds latency to choose the best path

These latencies are typically < 1% of typical IO service times Load balancing is more likely to be of benefit in SANs with heavy utilizations or

with intermittent errors that slow IOs on some path A round_robin algorithm is usually equivalent

Conclusion:Load balancing is unlikely to improve performance--especially when

compared to other strategies like algorithm=round_robin or approaches that balance IO with algorithm=fail_over

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29 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Balancing IOs with algorithm=fail_over

A fail_over algorithm can be efficiently used to balance IOs!► Any load_balancing algorithm must consume CPU and memory resources to determine

the best path to use.

► It's possible to setup fail_over LUNs so that the loads are balanced across the available FC adapters.

► Let's use an example with 2 FC adapters. Assume we correctly lay out our data so that the IOs are balanced across the LUNs (this is usually a best practice). Then if we assign half the LUNs to FC adapterA and half to FC adapterB, then the IOs are evenly balanced across the adapters!

► A question to ask is, “If one adapter is handling more IO than another, will this have a significant impact on IO latency?”

► Since the FC adapters are capable of handling more than 35,000 IOPS then we're unlikely to bottleneck at the adapter and add significant latency to the IO.

Page 30: Materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.3 Path Management and SAN Boot with MPIO on AIX John.

30 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

SDDPCM: An Overview

SDDPCM = Subsystem Device Driver Path Control Module

SDDPCM is MPIO compliant and can be used with IBM ESS, DS6000, DS8000, DS4000 (most models), DS5000, DS3950, V7000 and the SVC

► A “host attachment” fileset (populates the ODM) and SDDPCM fileset are both installed

► Host attachment: devices.fcp.disk.ibm.mpio.rte

► SDDPCM: devices.sddpcm.<version>.rte

LUNs show up as hdisks, paths shown with pcmpath or lspath commands► 16 paths per LUN supported

Provides a PCM per the MPIO architecture

One installs SDDPCM or SDD, not both.

SDDPCM is recommended and strategic

SDDPCM = Subsystem Device Driver Path Control Module

SDDPCM is MPIO compliant and can be used with IBM ESS, DS6000, DS8000, DS4000 (most models), DS5000, DS3950, V7000 and the SVC

► A “host attachment” fileset (populates the ODM) and SDDPCM fileset are both installed

► Host attachment: devices.fcp.disk.ibm.mpio.rte

► SDDPCM: devices.sddpcm.<version>.rte

LUNs show up as hdisks, paths shown with pcmpath or lspath commands► 16 paths per LUN supported

Provides a PCM per the MPIO architecture

One installs SDDPCM or SDD, not both.

SDDPCM is recommended and strategic

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31 © 2011 IBM Corporation

IBM Power Systems Technical Symposium 2011

Comparing AIX Default MPIO PCMs & SDDPCM

Feature/Function MPIO PCMs SDDPCM

How obtainedProvided as an integrated part of the base VIOS POWERVM firmware and AIX operating system product distribution

Provided by most IBM storage products for subsequent installation on the various server OS’s that the device supports

Suported DevicesSupports most disk devices that the AIX operating system and VIOS POWERVM firmware support, including selected third-party devices

Supports specific IBM devices and is referenced by the particular device support statement. The supported devices differ between AIX and POWERVM VIOS

OS Integration Considerations

Update levels are provided and are updated and migrated as a mainline part of all the normal AIX and VIOS service strategy and upgrade/migration paths

Add-on software entity that has its own update strategy and process for obtaining fixes. The customer must manage coexistence levels between both the mix of devices, operating system levels and VIOS levels. NOT a licensed program product.

Path Selection Algorithms

Fail over (default)Round Robin (excluding VSCSI disks)

Fail overRound RobinLoad Balancing (default)Load Balancing Port

Algorithm Selection Disk access must be stopped in order to change algorithm Dynamic

SAN boot, dump, paging support Yes Yes. Restart required if SDDPCM installed after

MPIOPCM and SDDPCM boot desired.

PowerHA & GPFS Support Yes Yes

Utilities standard AIX performance monitoring tools such as iostat and fcstat

Enhanced utilities (pcmpath commands) to show mappings from adapters, paths, devices, as well as performance and error statistics

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SDDPCM

Load balancing algorithms► rr - round robin

► lb - load balancing based on in-flight IOs per adapter

► fo - failover policy

► lbp - load balancing port (for ESS, DS6000, DS8000, V7000 and SVC only) based on in-flight IOs per adapter and per storage port

The pcmpath command is used to examine hdisks, adapters, paths, hdisk statistics, path statistics, adapter statistics, dynamically change the load balancing algorithm, and other administrative tasks such as adapter replacement, disabling paths

SDDPCM automatically recovers failed paths that have been repaired via the pcmserv daemon

► MPIO health checking can also be used, and can be dynamically set via the pcmpath command. This is recommended. Set the hc_interval to a non-zero value for an appropriate number of LUNs to check the physical paths.

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Path management with SDDPCM and the pcmpath command

# pcmpath query adapter# pcmpath query device# pcmpath query port# pcmpath query devstats# pcmpath query adaptstats# pcmpath query portstats# pcmpath query essmap# pcmpath set adapter …# pcmpath set device path …# pcmpath set device algorithm# pcmpath set device hc_interval# pcmpath disable/enable ports …# pcmpath query wwpnAnd more

SDD offers the similar datapath command

List adapters and statusList hdisks and pathsList DS8000/DS6000/SVC… portsList hdisk/path IO statisticsList adapter IO statisticsList DS8000/DS6000/SVC port statisticsList rank, LUN ID and more for each hdiskDisable/enable paths to adapterDisable/enable paths to a hdiskDynamically change path algorithmDynamically change health check intervalDisable/enable paths to a disk portDisplay all FC adapter WWPNs

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Path management with SDDPCM and the pcmpath command

# pcmpath query device …DEV#: 2 DEVICE NAME: hdisk2 TYPE: 2145 ALGORITHM: Load Balance SERIAL: 600507680190013250000000000000F4==========================================================================Path# Adapter/Path Name State Mode Select Errors 0 fscsi0/path0 OPEN NORMAL 40928736 0 1* fscsi0/path1 OPEN NORMAL 16 0 2 fscsi2/path4 OPEN NORMAL 43927751 0 3* fscsi2/path5 OPEN NORMAL 15 0 4 fscsi1/path2 OPEN NORMAL 44357912 0 5* fscsi1/path3 OPEN NORMAL 14 0 6 fscsi3/path6 OPEN NORMAL 43050237 0 7* fscsi3/path7 OPEN NORMAL 14 0…

• * Indicates path to passive controller• 2145 is a SVC which has active/passive nodes for a LUN• DS4000, DS5000, V7000 and DS3950 also have active/passive controllers• IOs will be balanced across paths to the active controller

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Path management with SDDPCM and the pcmpath command

# pcmpath query devstats

Total Dual Active and Active/Asymmetrc Devices : 67

DEV#: 2 DEVICE NAME: hdisk2=============================== Total Read Total Write Active Read Active Write MaximumI/O: 169415657 2849038 0 0 20SECTOR: 2446703617 318507176 0 0 5888

Transfer Size: <= 512 <= 4k <= 16K <= 64K > 64K 183162 67388759 35609487 46379563 22703724…

• Maximum value useful for tuning hdisk queue depths • “20” is maximum inflight requests for the IOs shown• Increase queue depth until queue is not filling up or

until IO services times suffer (bottleneck is pushed to the subsystem)• writes > 3ms• reads > 15-20ms

• See References for queue depth tuning whitepaper

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SDD & SDDPCM: Getting Disks configured correctly Install the appropriate filesets

► SDD or SDDPCM for the required disks (and host attachment fileset)► If you are using SDDPCM, install the MPIO fileset as well which comes with AIX

● devices.common.IBM.mpio.rte► Host attachment scripts

● http://www.ibm.com/support/dlsearch.wss?rs=540&q=host+scripts&tc=ST52G7&dc=D410 Reboot or start the sddsrv/pcmsrv daemon

smitty disk -> List All Supported Disk► Displays disk types for which software support has been installed

Or # lsdev -Pc disk | grep MPIOdisk mpioosdisk fcp MPIO Other FC SCSI Disk Drivedisk 1750 fcp IBM MPIO FC 1750 …DS6000disk 2105 fcp IBM MPIO FC 2105 …ESSdisk 2107 fcp IBM MPIO FC 2107 …DS8000disk 2145 fcp MPIO FC 2145 …SVCdisk DS3950 fcp IBM MPIO DS3950 Array Diskdisk DS4100 fcp IBM MPIO DS4100 Array Diskdisk DS4200 fcp IBM MPIO DS4200 Array Diskdisk DS4300 fcp IBM MPIO DS4300 Array Diskdisk DS4500 fcp IBM MPIO DS4500 Array Diskdisk DS4700 fcp IBM MPIO DS4700 Array Diskdisk DS4800 fcp IBM MPIO DS4800 Array Diskdisk DS5000 fcp IBM MPIO DS5000 Array Diskdisk DS5020 fcp IBM MPIO DS5020 Array Disk

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www-01.ibm.com/support/docview.wss?rs=540&uid=ssg1S7001350#AIXSDDPCM

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Migration from SDD to SDDPCM

Migration from SDD to SDDPCM is fairly straightforward and doesn't require a lot of time. The procedure is documented in the manual:1. Varyoff your SDD VGs2. Stop the sddsrv daemon via stopsrc -s sddsrv3. Remove the SDD devices (both vpaths and hdisks) via instructions below4. Remove the dpo device5. Uninstall SDD and the host attachment fileset for SDD6. Install the host attachment fileset for SDDPCM and SDDPCM 7. Configure the new disks (if you rebooted it's done, else run cfgmgr and

startsrc –s pcmserv)8. Varyon your VGs - you're back in business

To remove the vpaths and hdisks, use:

► # rmdev -Rdl dpo

No exportvg/importvg is needed because LVM keeps track of PVs via PVID

Effective queue depths change (and changes to queue_depth will be lost):► SDD effective queue depth = # paths for a LUN x queue_depth ► SDDPCM effective queue depth = queue_depth

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Multi-path code choices for DS4000/DS5000/DS3950

These disk subsystems might use RDAC, MPIO or SDDPCM► Choices depend on model and AIX level

MPIO is strategic► SDDPCM uses MPIO and is recommended

► SDDPCM not supported on VIOS yet for these disk subsystems so use MPIO SAN cabling/zoning is more flexible with MPIO/SDDPCM than with RDAC

► RDAC requires fcsA be connected to controllerA and fcsB connected to controllerB with no cross connections

These disk subsystems have active/passive controllers► All IO for a LUN goes to its primary controller

● Unless the paths to it fail, or the controller fails, then the other controller takes over the LUN

► Storage administrator assigns half the LUNs to each controller The manage_disk_drivers command is used to choose the multi-path code

► Choices vary among models and AIX levels DS3950, DS5020, DS5100, DS5300 use MPIO or SDDPCM

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Multi-path code choices for DS3950, DS4000 and DS5000

# manage_disk_drivers -lDevice Present Driver Driver Options2810XIV AIX_AAPCM AIX_AAPCM,AIX_non_MPIODS4100 AIX_SDDAPPCM AIX_APPCM,AIX_fcparrayDS4200 AIX_SDDAPPCM AIX_APPCM,AIX_fcparrayDS4300 AIX_SDDAPPCM AIX_APPCM,AIX_fcparrayDS4500 AIX_SDDAPPCM AIX_APPCM,AIX_fcparrayDS4700 AIX_SDDAPPCM AIX_APPCM,AIX_fcparrayDS4800 AIX_SDDAPPCM AIX_APPCM,AIX_fcparrayDS3950 AIX_SDDAPPCM AIX_APPCMDS5020 AIX_SDDAPPCM AIX_APPCMDS5100/DS5300 AIX_SDDAPPCM AIX_APPCMDS3500 AIX_AAPCM AIX_APPCM

To set the driver for use:# manage_disk_drivers -d <device> -o <driver_option>

AIX_AAPCM - MPIO with active/active controllers AIX_APPCM - MPIO with active/passive controllers AIX_SDDAPPCM - SDDPCM AIX_fcparray - RDAC

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Other MPIO commands for DS3/4/5000

# mpio_get_config –Av Frame id 0: Storage Subsystem worldwide name: 608e50017be8800004bbc4c7e

Controller count: 2 Partition count: 1 Partition 0: Storage Subsystem Name = 'DS-5020' hdisk LUN # Ownership User Label hdisk4 0 A (preferred) Array1_LUN1 hdisk5 1 B (preferred) Array2_LUN1 hdisk6 2 A (preferred) Array3_LUN1 hdisk7 3 B (preferred) Array4_LUN1 hdisk8 4 A (preferred) Array5_LUN1 hdisk9 5 B (preferred) Array6_LUN1

# sddpcm_get_config –Av output is the same as above

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XIV

Host Attachment Kit for AIXhttp://www-01.ibm.com/support/docview.wss?uid=ssg1S4000802

# lsdev -Pc disk | grep xivdisk 2810xiv fcp N/A

XIV support has moved from fileset support, to support within AIX► Installing the Host Attachment Kit is still recommended 

● Provides diagnostic and other commands  Disks configured as 2810xiv devices  ODM entries for XIV included with

AIX 5.3 TL 10, AIX 6.1 TL3, VIOS 2.1.2.x and AIX 7

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Nseries/NetApp Nseries/NetApp has a preferred storage controller for each LUN Not exactly an active/passive disk subsystem, as the non-preferred

controller can accept IO requests I/O requests have to be passed to the preferred controller which

impacts latency Install the SAN Toolkit

Ontap.mpio_attach_kit.*► Provides the dotpaths utility

and sanlun commands

► dotpaths sets hdisk path priorities to favor the primary controller

…for every IO going down secondary path, there will be 255 IOs sent down primary

path

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Storage Area Network (SAN) Boot

Boot Directly from SAN Storage is zoned

directly to the client HBAs used for boot

and/or data access Multi-path code for

the storage runs in client

SAN Sourced Boot Disks Affected LUNs are zoned

to VIOS(s) and assigned to clients via VIOS definitions

Multi-path code in the client will be the MPIO default PCM for disks seen through the VIOS.

Boot from an SVC Storage is zoned

directly to the client HBAs used for

boot and/or data access

SDDPCM runs in client (to support boot)

Boot from SVC via VIO Server

Affected LUNs are zoned to VIOS(s) and assigned to clients via VIOS definitions

Multi-path code in the client will be the MPIO default PCM for disks seen through the VIOS.

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Storage Area Network (SAN) Boot Requirements for SAN Booting

► System with FC boot capability

► Appropriate microcode (system, FC adapter, disk subsystem and FC switch)

► Disk subsystem supporting AIX FC bootSome older systems don’t support FC boot, if in doubt, check the sales manual

SAN disk configuration ► Create the SAN LUNs and assign them to the system's FC adapters’ WWPNs prior to

installing the system

► For non-MPIO configurations, assign one LUN to one WWPN to keep it simple

AIX installation► Boot from installation CD or NIM, this runs the install program

► When you do the installation you'll get a list of disks that will be on the SAN for the system

► Choose the disks for installing rootvg

► Be aware of disk SCSI reservation policies

● Avoid policies that limit access to a single path or adapter

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How to assure you install to the right SAN disk

Only assign the rootvg LUN to the host prior to install, assign data LUNs later, or Create a LUN for rootvg with a size different than other LUNs, or Write down LUN ID and storage WWN, or Use disk with an existing PVID

These criteria can be used to select the LUN from the AIX install program (shown in following screen shots) or via a bosinst_data file for NIM 

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Choose via Location Code

1 hdisk2 U8234.EMA.06EF634-V5-C22-T1-W50050768012017C2-L10000000000002 hdisk3 U8234.EMA.06EF634-V5-C22-T1-W500507680120165C-L20000000000003 hdisk5 U8234.EMA.06EF634-V5-C22-T1-W500507680120165C-L3000000000000

Storage WWN LUN ID

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Choose via Size

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Choose via PVID

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Storage Area Network Booting: Pros & Cons

The main benefits of SAN rootvg ► Performance < 2 ms write, 5-10 ms read due to cache. Higher IOPS► Availability with built in RAID protection ► Ability to easily redeploy disk► Ability to FlashCopy/MetroMirror the rootvg for backup/DR► Fewer hardware resources

SAN rootvg disadvantages► SAN problems can cause loss of access to rootvg ~ not an issue as app data is on SAN

anyway

► Potential loss of system dump and diagnosis if loss of access to SAN is caused by a kernel bug

► Difficult to change multi-path IO code

● Not an issue with dual VIOS—can take down one VIOS at a time and change multi-path code

SAN boot thru VIO with NPIV is like SAN boot

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Changing multi-path IO code for rootvg – not so easy

How do you change/update rootvg multi-path code when it’s in use? Changing from SDD to SDDPCM (or vice versa) requires contacting

support if booting from SAN, or:► Move rootvg to internal SAS disks, e.g., using extendvg, migratepv, reducevg,

bosboot and bootlist, or use alt_disk_install

► Change the multi-path code

► Move rootvg back to SAN

► Newer versions of AIX require a newer version of SDD or SDDPCM Follow procedures in the SDD and SDDPCM manual for upgrades of AIX

and/or the multi-path code Not an issue when using VIO with dual VIOSs

If one has many LPARs booting from SAN, one SAS adapter with a SAS disk or two can be used

to migrate SDD to SDDPCM, one LPAR at a time

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Documentation & References

Infocenter “Multiple Path IO” http://publib.boulder.ibm.com/infocenter/aix/v6r1/index.jsp?topic=/com.ibm.aix.baseadmn/doc/baseadmndita/dm_mpio.htm

SDD and SDDPCM Support matrix: www.ibm.com/support/docview.wss?rs=540&uid=ssg1S7001350

Downloads and documentation for SDD www.ibm.com/support/docview.wss?rs=540&context=ST52G7&dc=D430&uid=ssg1S4000065&loc=en_US&cs=utf-8&lang=en

Downloads and documentation for SDDPCM: www.ibm.com/support/docview.wss?rs=540&context=ST52G7&dc=D430&uid=ssg1S4000201&loc=en_US&cs=utf-8&lang=en

IBM System Storage Interoperation Center (SSIC)http://www-03.ibm.com/systems/support/storage/ssic/interoperability.wss

Guide to selecting a multipathing path control module for AIX or VIOShttp://www.ibm.com/developerworks/aix/library/au-multipathing/index.html

AIX disk queue depth tuning techdoc:http://www.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/TD105745

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Documentation & References

Hitachi MPIO Support Site

https://tuf.hds.com/gsc/bin/view/Main/AIXODMUpdates  EMC MPIO Support Site

ftp://ftp.emc.com/pub/elab/aix/ODM_DEFINITIONS/ HP Support Site

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?

lang=en&cc=us&objectID=c02619876&jumpid=reg_R1002_USEN HP StorageWorks for IBM AIX

http://h18006.www1.hp.com/storage/aix.html

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Session Evaluations

Session Number – SE39

Session Name – Working with San Boot…

Date - Thursday, April 28, 14:30, Lake Down B Friday, April 29, 13:00, Lake Hart B