RAID 5 functionality in the XP512 is the same as the XP256. RAID 5 requires four disks for an
array group. RAID 5 on the XP512 allows the data and parity to be split and distributed onto four disk drives using striping. Parity data for the group is created and stored on the parity stripe. Data can easily be recovered if a device in the parity group becomes inoperative or causes a read error.
In RAID 5 the striping size is set to that of a multiple of the block size that is transferred from cache. This allows the RAID controller to access each disk for a single stripe equivalence of data and allows the RAID controller to perform I/O operations on other disks in parallel, therefore increasing I/O performance substantially. In small scale or random I/O applications the data transfer rate remains the same as conventional RAID systems. In large or sequential I/O applications, RAID 5 permits the blocks in the same parity group to be processed in parallel, resulting in an increase in the data transfer rate. For small writes to single blocks, RAID 5 requires
extra reads from the data and parity disks before a small block can be written to the disk. Since the parity data is distributed on all disks in the group, it still allows parallel I/O processing of multiple
blocks.
Regards,
Mark
