Recovering from a two-drive failure in a RAID 10 configuration

In a RAID 10 configuration with four drives, data can be recovered if two of the drives fail. But recovering the data depends on which drives in the RAID configuration fail.

GlassHouse Technologies

In a RAID 10 configuration with four drives, can you recover data if two drives fail?

A RAID 10 configuration comprises two or more mirrored pairs of drives. Drives that are on each "side" of the mirror have data striped across them in a RAID 0 format. This combination of mirrored pairs ( RAID 1) and striping (RAID 0) is how RAID 10 gets its name. Because you must have at least two mirrored pairs to create a RAID 10 array, the minimum number of drives in a RAID 10 format has to be four.

So it's possible to recover data if two drives in a RAID 10 configuration fail, but it's dependent upon which two drives fail. Consider a four-drive RAID 10 setup where drives A and B have data striped across them and are mirrored by drives C and D on the opposite side. This RAID group can recover if any or all drives in a stripe fail, but not if both drives in a particular mirror fail. Therefore, we can recover if drives A and B or drives C and D fail, but not if drives A and C or drives B and D fail.

This was last published in September 2009

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