vtricks.com http://vtricks.com/?p=79 November 23, 2012 DataCore’s SANsymphony-V Part 1 – Disk Pools, Virtual Disks & Storage Allocation Units After my in troduction to DataCo re Softwa re and SA Nsymphon y-V this is th e first tech nical article of this se ries. This series isn’t meant to be a step by step guide, rather it should provide you with some basic knowledge on how SANsymphony-V works. Let’s start with disk pools and virtual disks. In the first step let’s look at disk pools in general. A disk pool as the name indicates pools together physical (backend) storage and allows to use the pool capacity to be used as a resource to create so called virtual disks. Virtual disks and disk pools have a tight relationship and that’s why a proper pool design is crucial to avoid performance issues. There are two possible approaches to pool storage resources. The classic approach is to use multiple pools to group disks with similar performance characteristics. The second option is to put all disks into a single disk pool and use a feature called “Auto-Tiering”. This enables SANsymphony-V to place and move blocks of data based between different types of storage. I’ll provide a separate post on “Auto-Tiering” tiering so I’ll skip that for now. The following screenshot depicts the available options when creating a new disk pool: Maximum number of tiers: This defines how many different types of storage (Tiers/performance classes) to pool will be made ofl. The number can be changed at any time. Storage allocation unit size: This setting could be seen as stripe size which will be striped across the attached psychical disks. DataCore calles them “Storage Allocation Units” (SAU). A single SAU can only reside on a single physical disk, a single SAU won’t be distributed across multiple disks. During the creation or afterwards physical disks can be added to the disk pool. When talking about phyiscal disks, I’m referring RAID volumes/arrays. Of course it’s also possible to use single disks of a JBOD, but to achieve a certain level of performance it’s recommended to use multiple disks within a RAID. Once the pool has been created and all space has been reclaimed (filled wit h zeros),the virt ual disks or vDisks can be carved up from the pool and served to the application hosts. Creating a vDisk is quite simple, all that is required the desired size and the disk pool. But what about the 128 MB SAU/stripe size? Even for me this initially sounded pretty big. SANsymphony-V stripes data across all off of the attached physical disks inside a disk pool.