VTrak E-Class Product Manual
290
The write policy automatically changes to Write Thru. When the battery comes
back online, the write policy automatically changes back to Write Back.
To enable the Adaptive Writeback Cache option, see “Making Controller Settings”
on page 122 or page 177.
Also see “Replacing a Cache Battery” on page 265.
Host Cache Flushing
When host cache flushing is enabled, the VTrak immediately flushes the data in
its controller cache to the drives when the Host sends a Flush Cache command.
Forced Read Ahead Cache
When forced read ahead cache is enabled, the controller cache is forced to read
ahead of the designated data. This action increases performance in video
applications, where large block sequential reads are common.
However, forced read ahead cache might reduce performance when large block
sequential reads do not occur. Promise recommends leaving this feature
disabled for applications other than video.
Cache Mirroring
VTrak subsystems with two controllers include a Cache Mirroring feature. Cache
Mirroring causes the local controller to mirror write data to the remote controller.
That means, when there is write data in the cache of the controller managing the
target logical drive, the same write data is copied to the cache of the other
controller as well. This arrangement protects the data from loss, in the event that
the local controller fails before the data is written to the logical drive.
Cache Mirroring works whether the write cache policy of your logical drives is set
to Write Back or Write Through. However, you only realize the advantage of
Cache Mirroring when the write cache policy is set to Write Back.
With Cache Mirroring enabled, any write data in the controller cache that has not
been written to the logical drive, will be written to the logical drive, even if the
controller fails. Enable Cache Mirroring when you require failover/failback
protection.
With Cache Mirroring disabled, any write data in the controller cache that has not
been written to the logical drive, will be lost if the controller fails. On the other
hand, write performance increases because of greater bandwidth. Disable Cache
Mirroring when you require maximum performance.
To use Cache Mirroring you must:
• Have two controllers in the subsystem
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