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Im using a PERC 3/DC controller to run a RAID 5 array using 4 hard disks. I am hoping to change this to 3 disks in the array and 1 hot spare. Is it possible to remove 1 disk from the array, reconfigure it as a hot spare, then reconfigure the RAID 5 array to use 3 disks WITHOUT loosing any data? I have backups but I would rather just reconfigure it without going through the hassle of restoring data. Thanks!

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up vote 4 down vote accepted

No, and if you have 4 disks and want two spares you are better off performance wise with a 4 disk RAID 10 instead of a 3 disk RAID 5 + hot spare. Either way your array will have 2 disks worth of usable capacity but the RAID 10 will have better write speeds and takes less time to recover from a failed disk.

Assuming the RAID 5 doesn't contain your boot volume, I'd go ahead and backup the data, reconfigure to a RAID 10, and restore the data.

    RAID Level Comparison for arrays up to 8 drives.
Features                RAID 0  RAID 1   RAID 5   RAID 6   RAID 10
Min Drives                2       2        3        4        4
Data Protection           0       1        1        2        2 (Up to one disk failure in each sub-array)
Read Performance         High    High     High     High     High
Write Performance        High   Medium    Low      Low     Medium
Degraded Read Perf       N/A    Medium    Low      Low      High
Degraded Write Perf      N/A     High     Low      Low      High
Capacity Utilization %   100     50      67-87    50-75     50
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+1 Agree. Many people don't event think about raid 10, but in some situations is the best way to go. – Pier Jun 4 '10 at 13:25
Thanks for confirming my suspicions, and thanks for the RAID 10 idea, it hadnt even crossed my mind. Il get on it first thing Monday. – scampbell Jun 4 '10 at 14:18

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