HUAWEI OceanStor Enterprise Unified Storage System ... · multipath framework of operating systems. UltraPath for AIX is a kernel driver developed based on the AIX MPIO mechanism.

HUAWEI OceanStor Enterprise Unified Storage System

UltraPath Technical White Paper

Issue 01

Date 2014-04-02

HUAWEI TECHNOLOGIES CO., LTD.

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Copyright © Huawei Technologies Co., Ltd. 2014. All rights reserved.

No part of this document may be reproduced or transmitted in any form or by any means without

prior written consent of Huawei Technologies Co., Ltd.

Trademarks and Permissions

and other Huawei trademarks are trademarks of Huawei Technologies Co., Ltd.

All other trademarks and trade names mentioned in this document are the property of their respective

holders.

Notice

The purchased products, services and features are stipulated by the contract made between Huawei and

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be within the purchase scope or the usage scope. Unless otherwise specified in the contract, all

statements, information, and recommendations in this document are provided "AS IS" without warranties,

guarantees or representations of any kind, either express or implied.

The information in this document is subject to change without notice. Every effort has been made in the

preparation of this document to ensure accuracy of the contents, but all statements, information, and

recommendations in this document do not constitute a warranty of any kind, express or implied.

Huawei Technologies Co., Ltd.

Address: Huawei Industrial Base

Bantian, Longgang

Shenzhen 518129

People's Republic of China

Website: http://enterprise.huawei.com

http://enterprise.huawei.com/

HUAWEI OceanStor Enterprise Unified Storage System UltraPath

Technical White Paper Contents

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Contents

1 List of Abbreviations .................................................................................................................... 1

2 Multipathing Software................................................................................................................. 2

2.1 Single Points of Failure and Multipathing .................................................................................................................... 2

2.2 Overview of Mainstream Multipathing Software ......................................................................................................... 3

2.3 Integrating Multipathing Software with Operating Systems......................................................................................... 5

3 Working Principle and Functions of UltraPath ....................................................................... 7

3.1 Typical Networking Diagrams ...................................................................................................................................... 7

3.1.1 Direct-Connection Networking .................................................................................................................................. 7

3.1.2 Dual-Switch Connection Networking ........................................................................................................................ 8

3.2 Working Principle ......................................................................................................................................................... 8

3.2.1 Integrating UltraPath with Operating Systems .......................................................................................................... 8

3.2.2 How to Identify and Manage Paths .......................................................................................................................... 10

3.2.3 How to Identify and Manage Path Groups............................................................................................................... 12

3.3 Functions of UltraPath ................................................................................................................................................ 13

3.3.1 Failover and Failback............................................................................................................................................... 13

3.3.2 Path Test ................................................................................................................................................................... 14

3.3.3 Load Balancing ........................................................................................................................................................ 14

4 Highlights of UltraPath .............................................................................................................. 16

4.1.1 All Paths Down Protection ....................................................................................................................................... 16

4.1.2 Isolation of Intermittently Faulty Paths ................................................................................................................... 17

4.1.3 Isolation of Links That Have Bit Errors ................................................................................................................... 17

4.1.4 Path Exception Alarming ......................................................................................................................................... 18

4.1.5 Automatic Host Registration .................................................................................................................................... 19

4.1.6 Path Disabling .......................................................................................................................................................... 20

4.1.7 Path Performance Monitoring and Status Statistics ................................................................................................. 20


UltraPath Technical White Paper 1 List of Abbreviations

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1 List of Abbreviations

Abbreviation Full Spelling Description

MPIO Multipath Input Output The native multipath framework of

mainstream operating systems is called

MPIO. MPIO allows storage vendors to

develop multipath solutions by inserting

adaptation modules to optimize

compatibility with their storage arrays.

PCM Path Control Module Adaptation module of the MPIO framework

in AIX.

DSM Device-Specific Module Adaptation module of the MPIO framework

in Windows.

PSA Pluggable Storage

Architecture

Multipath framework of the VMware ESX

platform.

MPP MultiPath Plug-In Multipath plug-in of the VMware ESX

platform.

NMP Native Multipath Plug-In Native multipath plug-in of the VMware ESX

platform. NMP is a scalable multipath

architecture. It can integrate the SATP and

PSP plug-ins.

SATP Storage Array Type

Plug-In

Storage array type plug-in that is used to

adapt to arrays of different vendors or models,

and masks the differences between arrays

from the NMP.

PSP Path Selection Plug-Ins Path selection plug-in, which implements

different path selection algorithms.


UltraPath Technical White Paper 2 Multipathing Software

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2 Multipathing Software

2.1 Single Points of Failure and Multipathing

A single point failure means that a certain point of a network is faulty, which may cause

network breakdown. In the following figure, a single point of failure may occur at:

1. The path between the external network and the application server

2. Application server

3. The path between the server and the storage controller

4. The storage controller

5. The path between the storage controller and disks

6. Disks

Figure 2-1 Single-path network

To prevent single points of failure, high-reliability systems implement redundant backup for

devices that may suffer single points of failure and adopt a cross-connection method to



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achieve optimal reliability. Meanwhile, redundant paths assist in achieving high performance,

as shown in the following figure.

Server

Switch Switch

Storage

Controller Controller

Multipathing software ensures reliability of redundant paths. If a path fails or cannot meet the

performance requirement, multipathing software automatically and transparently delivers I/Os

to other available paths to ensure that I/Os are transmitted effectively and reliably. As shown

in the following figure, multipathing software can handle host bus adapter (HBA) faults, link

faults, and controller faults.

2.2 Overview of Mainstream Multipathing Software

Currently, multipath solutions provided by storage vendors are classified into the following

types:



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1. Use self-developed multipathing software, for example, EMC PowerPath, HDS HDLM,

and Huawei UltraPath.

2. Provide storage adaptation plug-ins based on the multipath framework of operating

systems, for example, IBM and HP.

3. Use multipathing software built in operating systems (generally, A-A arrays or A-A/A

arrays that support ALUA support multipathing software built in operating systems).

For details about mainstream multipathing software, see the following table (the mainstream

operating systems of x86 servers, midrange computers, and virtualization platforms are

respectively Windows and Linux, AIX, and VMware ESX):

Item Windows Linux AIX VMware ESX

Multipathing

software built in

operating

systems

MPIO DM-Multipath MPIO NMP

Huawei UltraPath UltraPath UltraPath PCM

(based on

MPIO)

UltraPath

EMC PowerPath PowerPath PowerPath PowerPath

IBM1 SDDDSM

(based on

MPIO)

DM-Multipath SDDPCM

(based on

MPIO)

NMP

RDAC RDAC RDAC

HP2 SecurePath SecurePath SecurePath

DSM (based on

MPIO)

HP-DM HP-PCM

(based on

MPIO)

NMP

HDS HDLM HDLM HDLM HDLM

NetApp DSM (based on

MPIO)

DM-Multipath MPIO NMP

Veritas DMP DMP DMP DMP

RDAC is gradually replaced with SDD (an operating system framework plug-in).

SecurePath is gradually replaced with operating system framework plug-ins.

Multipathing software built in operating systems (often called MPIO) support the failover and

load balancing functions and can cope with scenarios that have moderate requirements on

reliability. Multipathing software developed by storage vendors is more professional and

delivers better reliability, performance, maintainability, and storage adaptation.



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2.3 Integrating Multipathing Software with Operating Systems

Multipathing software is a type of filter driver software running in host kernel mode. It can

block and process native disk creation/deletion and I/O delivery of operating systems. The

following figure shows the layer where the multipathing software resides.

HBA driver

SCSI layer

LVM

File system

Application

Multipath

Disk

Note: Generally, multipathing software works under the disk drive layer to provide virtual

disks for upper-layer application. Sometimes, the software works above the disk drive layer

but under the LVM layer (for example, mainstream multipathing software provided by the

Linux platform).

The following table lists the advantages and disadvantages of integrating multipathing

software with operating systems in various modes.



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Implementation Method

Advantage Disadvantage

Masking native disks

and creating virtual

SCSI disks

1. Secure. Users cannot use native

redundant disks, preventing data

corruption caused by misoperations.

2. Transparent to upper-layer

applications. Disks remain unchanged

before and after multipathing software

is deployed. Therefore, the

configurations of upper-layer

applications do not need to be

modified.

3. Better compatibility. Some

applications can identify only standard

SCSI disks.

Non-native multipathing software of

operating systems needs operating

system driver stacks to support the

filter driver mechanism to mask

native disks. Otherwise, some

operating system kernel functions

must be hooked, causing

coexistence with the third-party

driver.

Not masking native

disks and creating

additional virtual disks

Better compatibility with third-party

drivers. 1. Users can use native redundant

disks. Data corruption may be

caused due to misoperations.

2. The configurations of upper-layer

applications must be updated.

3. Incompatibility occurs.

UltraPath masks native disks to ensure data security.

The following table lists disks created using the preceding two implementation methods when

the Linux platform is used.

Single-Path Network Without Multipathing Software

Dual-Path Network Without Multipathing Software

Dual-Path Network with DM-MultiPath

Dual-Path Network with UltraPath

/dev/sdb /dev/sdb

/dev/sdc

sdb and sdc correspond to

the same LUN. Therefore,

concurrent access may

cause data corruption.

/dev/sdb

/dev/sdc

/dev/mpatha

It is secure to use mpatha, but

users may use sdb and sdc.

/dev/sdb

It is the same as that on a

single-path network.


UltraPath Technical White Paper 3 Working Principle and Functions of UltraPath

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3 Working Principle and Functions of UltraPath

3.1 Typical Networking Diagrams

3.1.1 Direct-Connection Networking



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3.1.2 Dual-Switch Connection Networking

UltraPath allows application servers to connect to storage arrays through Fibre Channel,

FCoE, and iSCSI ports.

3.2 Working Principle

3.2.1 Integrating UltraPath with Operating Systems

UltraPath is a type of filter driver software running in host kernel mode. It can block and

process native disk creation/deletion and I/O delivery of operating systems.

The following figure shows the layer where the UltraPath driver resides in Windows,

Linux, and Solaris.



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HBA driver

SCSI layer

LVM

File system

Application

Multipath

Disk

On the AIX and VMware ESX platforms, UltraPath is implemented based on the

multipath framework of operating systems.

UltraPath for AIX is a kernel driver developed based on the AIX MPIO mechanism.

MPIO is a device path management framework introduced in AIX 5.2 TL04, AIX 5.3,

and later versions to support multipath connection between a storage system and a host.

MPIO is presented as a device on the host.

MPIO employs Path-Control Modules (PCMs) to implement multipath management,

such as path adding or deleting, I/O path selection, path detection, and failover. The

following figure shows the relationship among the MPIO, PCM, and system.

Figure 3-1 Relationship among the AIX MPIO, PCM, and system

Application

Volume manager

File system

SCSI driver

MPIO

HBA driver

(UltraPath)

PCM KE

Path selection

Path adding

Path deletion

Device adding

Device deletion

……

UltraPath for VMware is a Multipath Plug-In (MPP) implemented based on the

pluggable storage architecture (PSA) in VMware vShpere/ESXi.

UltraPath senses path creation or deletion through functions registered with the PSA and

manages the paths.



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UltraPath invokes functions provided by the PSA to create or delete virtual logical

devices (that is, devices whose multiple paths are aggregated).

UltraPath receives I/Os from upper-layer applications through functions registered with

the PSA.

UltraPath invokes functions provided by the PSA to send I/Os.

ESX Server

VM VM VM VM VM

VM kernel

Pluggable storage architecture

UltraPath

NMP

SATP AA

SATP ALUA

SATP HDLM

PowerPath

On the VMware ESX platform, UltraPath can work together with NMP and other PSA-based

multipathing software (such as EMC PowerPath).

3.2.2 How to Identify and Manage Paths

Path

Each SCSI device has a SCSI address, which consists of an initiator ID (or host ID), bus ID,

target ID, and LUN. In actual networking, the initiator ID refers to the HBA port ID, and the

target ID refers to the controller port ID of a storage array (the bus ID can be the ID of an old

parallel SCSI bus, which is always 0 on a SAN). As shown in the following figure, two HBA

ports are connected to four controller ports. Two LUNs of the storage array are mapped to the

host. Therefore, eight SCSI devices are generated on the host and their SCSI addresses are:

I:1-B:0-T:1-L:1 (that is, initiator ID = 1, bus ID = 0, target ID = 1, and LUN = 1)

I:1 - B:0 - T:1 - L:2

I:1 - B:0 - T:3 - L:1

I:1 - B:0 - T:3 - L:2

I:2 - B:0 - T:2 - L:1

I:2 - B:0 - T:2 - L:2

I:2 - B:0 - T:4 - L:1

I:2 - B:0 - T:4 - L:2



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itch

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Sto

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Co

ntr

olle

r B

Co

ntr

olle

r A

HB

A 2

HB

A 1 Port 1

Port 2

Port 3

Port 4

LUN 1

LUN 2

Different SCSI devices mean using different paths to access different logical storage units.

Therefore, UltraPath abstracts paths based on SCSI devices. That is, one path points to one

SCSI device.

Note: As paths managed by UltraPath are associated with LUNs, UltraPath can process link

down failures between the host and storage array and failures to access a specific LUN

through a controller (for example, the storage array can use controller B instead of controller

A to access LUN 1).

Physical path

SCSI devices with the same initiator ID and target ID use the same I_T connection to access a

storage array. Therefore, UltraPath abstracts physical paths to associate these SCSI devices.

On the previous network, four physical paths can be virtualized:

I:1 - T:1

I:1 - T:3

I:2 - T:2

I:2 - T:4

Mapping between virtual disks and paths

Each LUN has a unique World Wide Name (WWN). UltraPath uses WWNs to

determine whether SCSI devices are LUNs or paths of a LUN.

UltraPath creates virtual disks that correspond to LUNs, provides the virtual disks for

upper-layer applications, and maintains the mapping between the virtual disks and paths.

As shown in the following figure, two paths exist between the storage array and the host,

three LUNs are mapped to the host, and six SCSI devices are generated on the host. UltraPath

determines that the six SCSI devices are from three LUNs through WWNs and creates three

virtual disks, each of which has two paths.



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3.2.3 How to Identify and Manage Path Groups

Path group

As a service processing unit of a storage array contains one or more controllers (or called

storage processors) and paths belonging to different controllers are associated, UltraPath

abstracts a path group to manage paths. As shown in the following figure, paths 1 and 2

belong to controller A, and paths 3 and 4 belong to controller B, forming two path groups.

Se

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Sw

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Sw

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Sto

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Co

ntr

olle

r B

Co

ntr

olle

r A

HB

A 2

HB

A 1 Path 1

Path 2

Path 3

Path 4

LUN 1

Path group 1

Path group 2

Active-active/Asymmetric array and path group priority



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For an active-active/asymmetric array, each LUN can be accessed by any controller. The

access efficiencies using different controllers are different. Generally, one LUN has a

preferred controller. The efficiency of accessing the LUN using its preferred controller is the

highest. Therefore, UltraPath identifies the preferred controller of a LUN and accesses the

LUN through the preferred controller. As shown in the following figure, the preferred

controller of LUN 1 is controller A. UltraPath selects paths 1 and 2 in path group 1 to access

LUN 1.

Se

rve

r

Sw

itch

Sw

itch

Sto

rag

e

Co

ntr

olle

r B

Co

ntr

olle

r A

HB

A 2

HB

A 1 Path 1

Path 2

Path 3

Path 4

LUN 1

Path group 1

Path group 2

3.3 Functions of UltraPath

3.3.1 Failover and Failback

Failover

UltraPath enables paths to fail over to functional paths. The following figure shows the

failover process.

1. An application delivers I/Os to the virtual disk created by UltraPath.

2. UltraPath forwards the I/Os to path 1(a SCSI device).

3. I/Os on path 1 fail due to a path fault.

4. UltraPath delivers I/Os to path 2.

5. Path 2 returns an I/O success acknowledgement.

6. UltraPath returns an I/O success acknowledgement to the application.



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Storage

HBA

Path 1

UltraPath

HBA

Path 2

Application

①

② ③ ④ ⑤

⑥

In step 3, the HBA tries reconnection for a period of time after a path is faulty. During the period of time,

I/Os remain in the HBA instead of returning back to UltraPath. For this reason, I/Os are blocked for a

period of time during the failover.

Failback

UltraPath automatically delivers I/Os to a path again after the path recovers from a fault.

There are two methods to recover a path:

1. For a hot-swappable system (for example, Windows), the SCSI device will be deleted if

the link between a host and a storage array is down. After the link is recovered, a SCSI

device will be created. UltraPath can immediately detect the path recovery.

2. For a non-hot-swappable system (for example, AIX or earlier versions of Linux),

UltraPath periodically tests and detects the path recovery.

3.3.2 Path Test

UltraPath tests the following paths in routine manner:

1. Faulty paths. UltraPath tests faulty paths with a high frequency to detect the path recover

as soon as possible.

2. Available but idle paths. UltraPath tests idle paths to identify faulty paths in advance,

preventing unnecessary I/O retires. The test frequency is kept low to minimize impact on

service I/Os.

3.3.3 Load Balancing

Load balancing is another critical feature of UltraPath. Load balancing enables UltraPath to

use the bandwidth of multiple links to improve overall system throughput.

UltraPath supports three load balancing algorithms:

− Round-robin: I/Os are evenly distributed onto each path.



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− Least-I/O: The number of queuing I/Os on each path is obtained and new I/Os are

delivered to the path with the least queuing I/Os.

− Least-block: The total amount of data on each path is obtained based on the least-I/O

algorithm and block size of each I/O request, and new I/Os are delivered to the

path with the least amount of data.

Paths involved in load balancing

For active-active arrays, UltraPath implements load balancing among all paths.

For active-active/asymmetric arrays, UltraPath implements load balancing in path groups. As

shown in the following figure, I/Os from LUN A are delivered to paths 1 and 2, and I/Os from

LUN B are delivered to paths 3 and 4:


UltraPath Technical White Paper 4 Highlights of UltraPath

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4 Highlights of UltraPath

4.1.1 All Paths Down Protection

In single-path networking, the HBA or iSCSI initiator tries reconnection for period of time

(30s or 60s) after a link is down. If the reconnection succeeds, I/Os continue to be sent

through the link. In multi-path networking, as a standby path is available, the retry period of

the HBA or iSCSI will be shortened to allow UltraPath to detect I/O failure and implement

failover quickly, shortening the I/O blocking time.

Application

Storage

HBA

Delivers I/Os.Reports an I/O

failure 60s later.

UltraPath

Storage

HBA 1

Delivers I/Os.

Reports an I/O

failure 5s later.

Application

HBA 2

Delivers I/Os

using another

path.1 2 1 2 3

If an All Paths Down (APD) issue occurs (usually single points of failure occur), service I/Os

may fail immediately and restarting switches will cause service interruption, as shown in the

following figure.

Server

Switch

Storage




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UltraPath implements a reconnection mechanism. If an APD issue occurs, UltraPath suspends

I/Os and tries to recover the path for period of time. If at least one path is recovered during the

period of time, the services can be recovered.

4.1.2 Isolation of Intermittently Faulty Paths

Application scenario

Links are intermittently disconnected due to poor link quality or incorrect connection.

Operations of UltraPath without isolation mechanisms

If a link is down, UltraPath delivers I/Os to another link and switches I/Os back after the

faulty link is recovered. The process repeats.

Impact on services without isolation mechanisms

If I/Os fail due to a link down failure, it takes time to switch I/Os to another path,

causing I/O blocking. If I/O blocking occurs frequently and repeatedly, the performance

of upper-layer services deteriorates or even services sensitive to I/O latency fail.

UltraPath uses the following mechanisms to isolate paths that are intermittently faulty:

− A path will not be used immediately after recovering from a fault, but stays in the

standby state for tests. I/Os will not be switched back to the path until the path passes

the tests.

− Times that a path fails are monitored. UltraPath sets the status of a path that fails for

several times to degraded, as shown in the following figure.

A degraded path is not unavailable but will not be used preferentially. The path will be used if no

optimal path is available.

4.1.3 Isolation of Links That Have Bit Errors


If the quality of a Fibre Channel link is poor, for example, an optical fiber is folded or

damaged or the power of an optical module decreases, bit errors may occur in the link.

Generally, bit errors do not cause link down, but I/Os time out or fail with a probability.

Operations of UltraPath without isolation mechanisms

After the path is

recovered,

services fail

back to the

original path.

A path is faulty for

the first time, and

services fail over to

another functional

path.

……

After the path is

recovered,

services do not

fail back to the

original path.

The path is faulty for n

times and the status of

the path is set to

degraded. Services fail

over to another functional

path.

…… …… ……

The path is

faulty for

the second

time and is

recovered...

Fault statistics period

Starting statistics

on fault times

Stopping statistics

on fault times



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− UltraPath retries if I/O errors occur. As I/Os on a link that has bit errors fail with a

probability, the retry can succeed. Therefore, UltraPath does not set the status of the

link to faulty.

− As links that have bit errors are congested more heavily, the least-I/O load balancing

algorithm lets UltraPath deliver fewer I/Os to the links to reduce the impact on

services. However, some I/Os will be delivered to the links.

Impact on services without isolation mechanisms

I/Os time out or fail with a probability. Although I/Os are successfully delivered after

several retires, I/Os are blocked during the reties. As a result, the performance of

upper-layer services deteriorates or even services sensitive to I/O latency fail.

− I/O timeout causes 60-second blocking of upper-layer services.

− I/Os that occasionally fail have an uncertain impact on upper-layer services. In

the worst cases, the performance of upper-layer services drops by more than 90%.

UltraPath employs multiple mechanisms to efficiently isolate links that have bit errors.

− UltraPath identifies unhealthy paths based on the I/O latency, failure rate, and

collected statistics and sets their status to degraded. These paths will not be used

preferentially.

− As I/Os on links that have bit errors fail with a probability, these I/Os must be tested

strictly for a long time. UltraPath constructs I/Os sensitive to bit errors to

continuously check degraded paths, ensuring that links that have bit errors are

isolated.

The frequency of bit error test bit streams is limited to prevent impact on applications.

4.1.4 Path Exception Alarming

If a path fails, UltraPath automatically switches service I/Os to another path to ensure service

continuity. However, this is insufficient. System reliability decreases and risks of single points

of failure exist. As shown in the following figure, when one switch is faulty, the other switch

and the optical fiber between the host and switch become the single points.

Server

Switch Switch

Storage


In this case, maintenance personnel must recover the faulty component as soon as possible to

restore system reliability.

UltraPath allows path-related alarms to be sent to Huawei storage arrays in in-band mode.

Then the storage arrays centrally manage the alarms and send the alarms by emails or short

messages, or notify the third-party network management software.



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Server

Switch Switch

Storage

Pushing alarms using

an available path

Short

messagesEmails ISM SNMP

The alarm mechanism of UltraPath has the following characteristics:

No socket-based agents need to be installed on service hosts. No network ports are

occupied. No security vulnerabilities exist.

No SNMP traps need to be configured on service hosts. This simplifies

configurations when a large number of service hosts are deployed.

UltraPath supports the following path exceptions:

− Paths are unavailable.

− Paths are degraded (links have bit errors or are intermittently faulty).

− No redundant controllers are connected to paths (including that the initial networking

is incorrect).

The alarm function of UltraPath is designed for scenarios where system reliability decreases, not for

scenarios where all paths are faulty. When all paths are faulty, services are interrupted or stopped.

4.1.5 Automatic Host Registration

After a storage array is connected to a host, host-related configuration must be performed.

The host information pushing function of UltraPath can help with the configuration,

simplifying the configuration and reducing configuration errors.

To manually register a host with a storage array, perform the following steps (connecting

storage through iSCSI on the Linux platform is used as an example):

1. On the ISM, manually create a logical host named webserver1 for the storage array

and set the host type to Linux.

2. Log in to the service host and query and record the iSCSI initiator IQN:

# cat /etc/iscsi/initiatorname.iscsi

InitiatorName= iqn.1996-04.de.suse:01:d9a41f41c999tt

3. On the ISM, select port iqn.1996-04.de.suse:01:d9a41f41c999tt recorded in step 2

and add it for logical host webserver1.

The procedure for automatically registering a host using UltraPath is as follows:

1. UltraPath uses in-band commands to send information such as the host operating

system type (Linux), host name (webserver1), IP address, and UUID to Huawei

storage arrays over all links.



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2. Logical host webserver1 is automatically created based on the information sent by

UltraPath. The host type is automatically set to Linux. All initiator ports that send

the host information are automatically added to logical host webserver1.

Comparison between the two methods:

1. The traditional method is complicated especially when a large number of hosts or

ports exist. Meanwhile, configuration errors may occur, such as host type selection

errors and initiator port adding errors.

2. UltraPath-based automatic host registration can be implemented without manual

operation. In addition, the configuration information is consistent with the physical

environment.

4.1.6 Path Disabling


Replacement of planned components, such as HBAs, optical modules, and interface modules

Impact when no manual path disabling is available

− If a component is directly removed, I/Os may fail. Although UtraPath can switch I/Os

to other paths, I/O blocking exists, affecting upper-layer services.

− Some HBAs can be securely removed only when they are not working.

UltraPath supports the following path disabling:

1. Disable a specified path group when a controller is replaced or repaired.

2. Disable a specified physical path that is identified by the HBA port plus target port

ID.

4.1.7 Path Performance Monitoring and Status Statistics

UltraPath supports various path performance monitoring and status statistics functions:

LUN- or path-based performance monitoring

Monitoring for IOPS, bandwidth, and latency

Separate monitoring for reads and writes

Statistics on the numbers of queuing I/Os, I/O retries, and faults

HUAWEI OceanStor Enterprise Unified Storage System ... · multipath framework of operating systems. UltraPath for AIX is a kernel driver developed based on the AIX MPIO mechanism.

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