Write/Read cache streaming mode
: When the cache streaming mode is active, the system
continuously flushes the cache memory, which provides maximum cache buffering to protect against
delayed command responses. When the streaming mode is not active, the system runs with a full cache,
which helps reduce disk access and maximizes random I/O performance.
Preemptive write-before-read flushing
: When preemptive write-before-read flushing is active, the
system automatically flushes all outstanding write commands from the cache to the disks prior to reading
data.
Generate warnings from drive heuristics
: When this setting is enabled, the system will raise a warning-
level log message and beacon any drive passing a preset threshold level based on the rate of media retries,
the drive I/O response time, and other key drive metrics.
Note
This is a heuristic diagnostic tool. If you wish to use it, please seek advice from Nexsan support (see
SCSI third-party copy extensions (requires reboot)
: This setting enables support for the SCSI (LID1)
third-party copy extensions, and the WRITE SAME and COMPARE AND WRITE commands. If
supported, these can be used by the host operating system to accelerate some storage functions (for
example, migrating data within an array or zeroing blocks). Changing this setting requires a system reboot
(see
Cache optimization setting
: This setting tells the write cache how best to access data for your particular
data usage. There are three settings:
Random access
: This setting is best for systems that access a large number of files or many different
areas of its volumes, such as systems with many individual users or that house frequently accessed
databases.
Mixed sequential/random
(default): This setting is best for systems that are “mixed use”, sometimes
accessing many smaller files and sometimes accessing a few larger files.
Sequential access
: This setting is best for systems that access a small number of large files
sequentially, such as an archive of manuscripts or videos.
Note
This setting can be changed in real-time. We encourage you to experiment with this setting to
determine which configuration works best for your environment.
►
To configure the write cache:
1. Enable or disable the write cache by selecting
Enabled
or
Disabled
for
Desired write cache state
.
Note
To force the write cache into the desired state without having to reboot the system, use the
Manually override current write cache status
check box.
2. Do one of the following:
To allow hosts to issue commands that force the write cache to not be used, check the
Allow
attached host to override write cache configuration
check box.
To prevent hosts from issuing commands that force the write cache to not be used, uncheck the
Allow attached host to override write cache configuration
check box.
3. Do one of the following:
To prevent “forced unit access” commands from bypassing the cache, check the
Ignore force unit
access (FUA) bit
check box.
To allow “forced unit access” commands to bypass the cache, uncheck the
Ignore force unit access
(FUA) bit
check box.
Chapter 3: The Graphical User Interface — System Administration
Nexsan High-Density Storage
User Guide
190