Raid 1 (Mirroring) - Fantec SQ-X2RU3e User Manual

RAID 1 (Mirroring):

The RAID1 storage policy stores all data in duplicate on separate drives to protect
against data loss due to drive failure. One drive mirrors the other at all times.
Every write operation goes to both drives. RAID1 provides the highest level of data
protection for critical data that you cannot afford to lose if a hard drive fails, but halves
the amount of storage capacity because all data must be stored twice. The resulting
storage capacity of the virtual RAID1 volume will be equivalent to the size of one hard
drive (if both drives are the same) or the smaller of the two drives (if they are different).
If one drive fails, the RAID1 volume is still usable, but it is in a vulnerable state because
its mirrored hard drive is inaccessible. When the offline drive comes back online, the
appliance begins a rebuild process immediately to restore data redundancy. Although
the volume remains available during the rebuild process, the volume is susceptible to
data loss through damage to the remaining drive until redundancy is restored at the end
of the rebuild and verification process. Host access takes precedence over the rebuild
process. If you continue to use the SAFE volume during the rebuild, the rebuild process
will take a longer time to complete, and the host data transfer performance will also be
affected.
Drive A
250GB
RAID1
250GB
FANTEC SQ-X2RU3e
Port 0 Port 1
Drive B
250GB
Equal hard drives
FANTEC SQ-X2RU3e
Port 0
Drive A
250GB
Unequal hard drives
11
RAID1
250GB
Port 1
Drive B
750GB