MicroNet Technology MaxNAS - Manual (Page 54)

MaxNAS Owner’s Manual 54
RAID 6
Also known as dual parity, RAID 6 is similar to
RAID 5, but offers double the fault tolerance
by performing two parity computations on
overlapping subsets of the data. RAID 6 offers
fault tolerance greater that RAID 1 or RAID
5 but only consumes the capacity of 2 disk
drives for distributed parity data. RAID 6 is
an extension of RAID 5 that uses a second
independent distributed parity scheme. Data is
striped on a block level across a set of drives,
and then a second set of parity is calculated
and written across all of the drives.
Pros: Very good general transfer performance
Fault tolerant
Cons: Can be slow at large size file transfers
Hot Swappable Disk support
Your MaxNAS has a built in protection circuit to support replacement of disk drives without
having to shut down or reboot the RAID. In case of drive failure, the failed drive can be
removed from the MaxNAS and replaced with a new drive without disrupting dataflow to the
host computer.
Hot Spare Drives
A hot spare drive is an unused online available drive, which is ready for replacing a failed
disk drive. In a RAID level 1 or 5 RAID set, any unused online available drive installed but not
belonging to a RAID set can be defined as a hot spare drive. Hot spares permit you to replace
failed drives automatically without powering down your MaxNAS. When your MaxNAS detects
a drive failure, the system will automatically and transparently rebuild using any available hot
spare drive(s). The RAID set will be reconfigured and rebuilt in background, while the RAID
subsystem continues to handle system requests. During the automatic rebuild process, system
activity will continue as normal, but system performance and fault tolerance will be affected.
Hot-Swap Disk Rebuild
A Hot-Swap function can be used to rebuild disk drives in arrays with data redundancy such
as RAID level 1(0+1), 3, and 5. If a hot spare is not available at time of drive failure, the failed
disk drive must be replaced with a new disk drive so that the data on the failed drive can
be rebuilt. If a hot spare is available, the rebuild starts automatically when a drive fails. The
RAID subsystem automatically and transparently rebuilds failed drives in the background with
user-definable rebuild rates. The RAID subsystem will automatically restart the system and
the rebuild if the system is shut down or powered off abnormally during a reconstruction
procedure condition. Please note that the system may no longer be fault tolerant during
degraded operation or the rebuild process- Fault tolerance will be lost until the damaged drive
is replaced and the rebuild operation is completed.
5-Understanding RAID