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FAST (RAID 0)
The FAST storage policy, also
called striping or RAID 0,
presents the best data speed
by using both disks in parallel.
Hard drive data segments
are written to different
disks simultaneously which
increases performance, but
at an increased fault sensitivity
(two drive's worth of data may
be lost at a single disk fault.)
The FAST storage policy creates a single virtual volume that
is striped across both hard drives, with a storage capacity
that is equal to the sum of both hard disk drives.
SAFE (RAID 1)
The SAFE storage policy
stores all data in duplicate on
each drives to protect against
data loss due to drive failure.
One drive mirrors the other
at all times, which means
every write operation goes to
both drives. SAFE provides
the highest level of data fault
tolerance, but halves the amount of storage capacity because
all data must be stored twice. The resulting storage capacity
of the virtual SAFE volume will be equivalent to the size of
one hard drive. If one drive fails, the SAFE volume is still
usable, but it is in a vulnerable state because its mirrored
hard drive is inaccessible. When the offline drive is replaced,
the Megadisk will 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.
SAFE33 and SAFE50
The SAFE33 and SAFE50 storage
policies create two virtual volumes;
one SAFE volume and one BIG volume.
RAID33 creates a SAFE partition
on 33% of the available space, and
SAFE50 creates a safe partition on
50% of the available spare. The BIG
partition utilizes the remaining capacity. These policies
should be used when you need the high reliability for some
of your data (with the added overhead of mirroring) but
maximum space for the remainder of your data, reducing the
cost of additional hard drives in operations where non-critical
data could be lost without severe consequences. SAFE33
and SAFE50 use a SAFE volume that is mirrored across two
hard drives to protect your critical data in the event a hard
drive failure. If one drive fails the SAFE volume is retrievable
although the BIG volume is not. When you replace the failed
drive, the SAFE volume is automatically rebuilt on to the
replacement drive.
SAFE33 and SAFE50 should only be used with a port
multiplier enabled SATA host controller such as the
MicroNet SATAPCIX4 eSATA-PCIX host bus adapter, or the
MicroNet SATAPCIE2 eSATA-PCI Express host bus adapter.
If used with a non PM-aware eSATA host bus adapter, only a
single drive is presented (drive 0). No such limitation exists
if using a USB host connection.
