Protection provided by RAID and SyncMirror

Combining RAID and SyncMirror provides protection against more types of drive failures than using RAID alone.

You can use RAID in combination with the SyncMirror functionality, which also offers protection against data loss due to drive 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 drive failure in one plex is repaired by the undamaged data in the other plex.

For more information about SyncMirror, see the Data ONTAP Data Protection Online Backup and Recovery Guide for 7-Mode.

The following tables show the differences between using RAID alone and using RAID with SyncMirror:

Table 1. RAID-DP and SyncMirror
Criteria	RAID-DP alone	RAID-DP with SyncMirror
Failures protected against	Single-drive failure Double-drive failure within a single RAID group Multiple-drive failures, as long as no more than two drives 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 drive failures within a single RAID group Storage subsystem failures (HBA, cables, shelf) that lead to three or more concurrent drive failures within a single RAID group	Three or more concurrent drive failures in a single RAID group on both plexes
Required resources per RAID group	`n` data drives + 2 parity disks	2 x (`n` data drives + 2 parity drives)
Performance cost	Almost none	Low mirroring overhead; can improve performance
Additional cost and complexity	None	SyncMirror license and configuration

Table 2. RAID4 and SyncMirror
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 drive failures within a single RAID group Storage subsystem failures (HBA, cables, shelf) that lead to two or more concurrent drive failures within a single RAID group	Two or more concurrent drive failures in a single RAID group on both plexes
Required resources per RAID group	`n` data drives + 1 parity drive	2 x (`n` data drives + 1 parity drive)
Performance cost	None	Low mirroring overhead; can improve performance
Additional cost and complexity	None	SyncMirror configuration and extra storage requirement

Table 3. RAID0 and SyncMirror
Criteria	RAID0 alone	RAID0 with SyncMirror
Failures protected against	No protection against any failures RAID protection is provided by the RAID implemented on the storage array.	Any combination of array LUN, connectivity, or hardware failures, as long as only one plex is affected
Failures not protected against	No protection against any failures RAID protection is provided by the RAID implemented on the storage array.	Any concurrent failures that affect both plexes
Required array LUN resources per RAID group	No extra array LUNs required other than `n` data array LUNs	2 x `n` data array LUNs
Performance cost	None	Low mirroring overhead; can improve performance
Additional cost and complexity	None	SyncMirror configuration and extra storage requirement