Dell PowerVault MD3820f - Manual (Page 115)

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Disk Pools And Disk Pool Virtual Disks
Disk pooling allows you to distribute data from each virtual disk randomly across a set of physical disks.
Disk pooling provides RAID protection and consistent performance across a set of physical disks logically
grouped together in the storage array. Although there is no limit on the maximum number of physical
disks that can comprise a disk pool, each disk pool must have a minimum of 11 physical disks.
Additionally, the disk pool cannot contain more physical disks than the maximum limit for each storage
array. The physical disks in each disk pool must:
• be SAS or nearline SAS
• have the same physical disk speed (RPM)
NOTE: The maximum physical disk speed is 15,000 rpm for standard SAS and 7,500 rpm for 3.5"
nearline SAS.
NOTE: In a disk pool, the physical disks must have the same capacities. If the physical disks have
different capacities, the MD Storage Manager uses the smallest capacity among the physical
disks in the pool. For example, if your disk pool is comprised of several 4 GB physical disks and
several 8 GB physical disks, only 4 GB on each physical disk is utilized.
The data and redundancy information in a disk pool is distributed across all of the physical disks in the
pool and provides the following benefits:
• Simplified configuration
• Better utilization of physical disks
• Reduced maintenance
• the ability to use thin provisioning
Difference Between Disk Groups And Disk Pools
Similar to a disk group, you can create one or more virtual disks in a disk pool. However, the disk pool
differs from a disk group in the way data is distributed across the physical disks comprising the pool.
In a disk group, data is distributed across the physical disks based on RAID level. You can specify a RAID
level when you create the disk group, then the data for each virtual disk is written sequentially across the
set of physical disks comprising the disk group.
NOTE: Because disk pools can co-exist with disk groups, a storage array can contain both disk
pools and disk groups.
Disk Pool Restrictions
CAUTION: If you downgrade the RAID controller module firmware version of a storage array that
is configured with a disk pool to a firmware version that does not support disk pools, the virtual
disks are lost and the physical disks are treated as unaffiliated with a disk pool.
• All physical disk media types in a disk pool must be the same. Solid State Disks (SSDs) are not
supported.
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