Grass Valley Network Attached Storage System Serial ATA Network User Guide v.1.0.04 - Manual (Page 149)

Chapter 10 RAID System Administration
148 Digital News Production
Set RAID Controller Defaults
No window appears with this command. To reset defaults, choose Storage |
RAID System | Controller | Set Defaults . The RAID controller caching fields
are immediately reset to the values described in this table:
Field Default Description
Read Cache Enable When read cache is enabled, the controller checks cache
memory for the requested data. If it finds the data in
cache, it returns that data. Only if the data is not in cache
does it read the drives. When read cache is disabled, data
is always read from the drives.
Write Cache Enabled in a
single controller
Disabled in a
dual controller
When write cache is enabled, the controller saves the
data in cache memory and returns a Command Complete
before actually writing the data to the drives. When write
cache is disabled, the controller writes the data to the
drives before issuing a Command Complete. Enabling
write cache increases write performance, but introduces
some data vulnerability. If data integrity is the primary
consideration, disable write cache. In a single controller
configuration, enabling write cache will increase write
performance.
Write Cache
Mirroring Disabled This feature is available only in a dual controller system,
and enabling it on one controller automatically enables it
on the other controller. When write cache mirroring
(WCM) is enabled, write cache data is duplicated in
cache memory of each controller. WCM protects data
when one controller fails because the data can be found
in the other controller's memory. Exactly half of the
write segments on each controller are reserved for the
peer controller data. With write cache mirroring enabled,
static cache segment allocation is automatically enabled
and cannot be disabled. With write cache mirroring
enabled, write caching is allowed when both controllers
are enabled. The number of write segments (see below)
is not changed when WCM is enabled or disabled. Half
of the write segments in each controller are reserved for
the mirrored data.
Multiplication
Factor Disabled When the multiplication factor is enabled, maximum
prefetch is overridden. Instead, the largest number of
blocks that can be prefetched when multiplication factor
is enabled is (maximum prefetch) x (length of the current
Read command). The number of blocks that can be
prefetched is also limited by the maximum prefetch
ceiling.