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Storage : Aggregates : Understanding aggregates : Considerations for sizing RAID groups for disks
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:
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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.
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Your RAID groups should be between 12 and 20 disks.
The reliability of SAS and FC disks can support a RAID group size of up to 24 if needed.
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If you can satisfy the above two requirements with multiple RAID group sizes, choose the larger size.
For SSDs, you still want to have the most even layout possible, as for HDDs, but the recommended range of RAID group size is between 20 and 28.

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