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Cluster-Mode System Manager Help : Cluster-Mode : Cluster > 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.
In most cases, the default RAID group size is the best size for your RAID groups. However, you can change the maximum size of your RAID groups.
Note: You change the size of RAID groups on a per-aggregate basis. You cannot change the size of an individual RAID group.
Configuring an optimum RAID group size for an aggregate requires a trade-off of factors. Adding more data disks to a RAID group increases the striping of data across those disks, which typically improves I/O performance. Additionally, a smaller percentage of disks is used for parity rather than data. However, with more disks in a RAID group, there is a greater risk that one of the disks might fail.
Note: With RAID-DP, you can use larger RAID groups because they offer more protection. A RAID-DP group is more reliable than a RAID4 group that is half its size, even though a RAID-DP group has twice as many disks. Thus, the RAID-DP group provides better reliability with the same parity overhead.
Large RAID group configurations offer the following advantages:
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More data drives available. An aggregate configured into a few large RAID groups requires fewer drives reserved for parity than that same aggregate configured into many small RAID groups.
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Small improvement in storage system performance. Write operations are generally faster with larger RAID groups than with smaller RAID groups.
Small RAID group configurations offer the following advantages:
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Shorter disk reconstruction times. In case of disk failure within a small RAID group, data reconstruction time is usually shorter than it would be within a large RAID group.
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Decreased risk of data loss due to multiple disk failures. The probability of data loss through double-disk failure within a RAID4 group or through triple-disk failure within a RAID-DP group is lower within a small RAID group than within a large RAID group.