RAID5 volume

A RAID-5 volume dedicates the equivalent of the space of one disk in the RAID-5 volume for storing the parity stripes, but distributes the parity stripes across all the disks in the group. The data and parity information are arranged on the volume so that they are always on different disks.Implementing a RAID-5 volume requires a minimum of three and a maximum of 32 disks in the set. The physical disks do not need to be identical. However, there must be equal size blocks of unused space available on each physical disk in the set. The disks can be on the same or different controllers. As with striped volumes, you cannot add disks to a RAID-5 volume if you need to increase the size of the volume later.If one of the disks in a RAID-5 volume fails, none of the data is lost. When a read operation requires data from the failed disk, the system reads all of the remaining good data stripes in the stripe and the parity stripe. Each data stripe is subtracted (with XOR) from the parity stripe; the order is not important. The result is the missing data stripe.When the system needs to write a data stripe to a disk that has failed, it reads the other data stripes and the parity stripe and backs them out of the parity stripe, leaving the missing data stripe. The modifications needed to the parity stripe can now be calculated and made. Because the data stripe is unavailable, it is not written; only the parity stripe is written.There is no effect on a read operation when the disk that failed contains a parity stripe. (The parity stripe isn't needed for a read, unless there is a failure in a data stripe.) When the failed disk contains a parity stripe, the system does not compute or write the parity stripe when there is a change in a data stripe.

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