Symmetrix
For the last time – Raid-S does not mean “STRIPED”
by Jesse on Sep.22, 2006, under RAID, Symmetrix
RAID-S isn’t striped. If it were it would be Raid-5.
EMC utilized Raid-S as a stop-gap to the fact that they didn’t offer Raid5. (the constant XOR computations slowed down performance – until the faster DMX line came up which now allows for both 3+1 and 7+1 raid5.
Raid-S takes three volumesand computes a parity bit based on them, but lets them maintain their separate identities.
so SYMDEV1, SYMDEV2, and SYMDEV3 each have data, and can be mounted as /u01, /u02, and /u03. If a volumeis lost, that volume’s data is extrapolated from the parity volume. If two volume are lost (either two data volumes or one data volume and one parity volume) the data on the third (or remaining two in the event of a parity volume failure)
This actually gives you an added level of protection in that you don’t lose the entire group on the failure of multiple volumes as you do in Raid5.
Note I said volumes and not disks. Raid-S volumes are hypervolumes (or partitions) of disks and not whole physical disks.
