Combining RAID and SyncMirror provides protection against more types of disk failures than using RAID alone.
RAID4 and RAID-DP can be used in combination with the Data ONTAP SyncMirror feature, which also offers protection against data loss due to disk or other hardware component failure. SyncMirror protects against data loss by maintaining two copies of the data contained in the aggregate, one in each plex. Any data loss due to disk failure in one plex is repaired by the undamaged data in the opposite plex.
For more information about SyncMirror, see the Data Protection Online Backup and Recovery Guide.
The following tables outline the differences between using RAID alone and using RAID with SyncMirror.
| Criteria | RAID-DP alone | RAID-DP with SyncMirror |
|---|---|---|
| Failures protected against | Single-disk failure
Double-disk failure within a single RAID group Multiple-disk failures, as long as no more than two disks within a single RAID group fail |
All failures protected against by RAID-DP alone
Any combination of failures protected against by RAID-DP alone in one plex, concurrent with an unlimited number of failures in the other plex Storage subsystem failures (HBA, cables, shelf), as long as only one plex is affected |
| Failures not protected against | Three or more concurrent disk failures within a single RAID group
Storage subsystem failures (HBA, cables, shelf) that lead to three or more concurrent disk failures within a single RAID group |
Three or more concurrent disk failures in a single RAID group on both plexes |
| Required disk resources per RAID group | n data disks + 2 parity disks | 2 x (n data disks + 2 parity disks) |
| Performance cost | Almost none | Low mirroring overhead; can improve performance |
| Additional cost and complexity | None | SyncMirror license and configuration |
| Criteria | RAID4 alone | RAID4 with SyncMirror |
|---|---|---|
| Failures protected against | Single-disk failure
Multiple-disk failures, as long as no more than one disk within a single RAID group fails |
All failures protected against by RAID4 alone
Any combination of failures protected against by RAID4 alone in one plex, concurrent with an unlimited number of failures in the other plex Storage subsystem failures (HBA, cables, shelf), as long as only one plex is affected |
| Failures not protected against | Two or more concurrent disk failures within a single RAID group
Storage subsystem failures (HBA, cables, shelf) that lead to two or more concurrent disk failures within a single RAID group |
Two or more concurrent disk failures in a single RAID group on both plexes |
| Required disk resources per RAID group | n data disks + 1 parity disk | 2 x (n data disks + 1 parity disk) |
| Performance cost | None | Low mirroring overhead; can improve performance |
| Additional cost and complexity | None | SyncMirror license and configuration |