Considerations for sizing RAID groups for disks

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Considerations for sizing RAID groups for disks

Configuring an optimum RAID group size for an aggregate made up of disks requires a trade-off of factors. You must decide which factor—speed of recovery, assurance against data loss, or maximizing data storage space—is most important for the aggregate that you are configuring.

You change the size of RAID groups on a per-aggregate basis. You cannot change the size of an individual RAID group.

You should follow these guidelines when sizing your RAID groups for HDD disks:

•	All RAID groups in an aggregate should have the same number of disks.

If this is impossible, any RAID group with fewer disks should have only one less disk than the largest RAID group.

•	The recommended range of RAID group size is between 12 and 20.

The reliability of SAS and FC disks can support a RAID group size of up to 28 if needed.

•	If you can satisfy the first two guidelines with multiple RAID group sizes, you should choose the larger size.

You should follow these guidelines when sizing your RAID groups for SSD disks:

•	All RAID groups in an aggregate should have the same number of disks.

If this is impossible, any RAID group with fewer disks should have only one less disk than the largest RAID group.

•	The recommended range of RAID group size is between 20 and 28.

For Flash Pools, the SSD tier must have the same RAID group size as the HDD tier. You should use the HDD guidelines to determine the RAID group size for the entire Flash Pool.

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