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Adaptec CI/O Management Software User's Guide
Write Caching
There are two Write caches: the Write-back Cache and the Write-
through Cache. Options for these caches can be adjusted separately
for each array.
Write-back Caching— this option defines the maximum Write
command size (stated as a number of data blocks) that will be
cached in the Write-back Cache. When the Write command is
issued, the data is quickly written to the cache and a write
completed status is sent to the host system. When the buffer is
needed or when there is free time on the bus, the data is
written from the cache to the disk. For example, if Write-back
Caching is set to 4 blocks and the operating system issues a
command to write up to 4 blocks of data, the data is stored in
the Write-back Cache until it can be written to disk. However,
if the operating system issues a Write command for 5 (or more)
blocks of data, nothing is stored in the Write-back Cache and
the data is instead written immediately to the disk.
Caution:
It is possible for data to be lost if the power to
!
the system is interrupted while the data is in the
Write-back Cache, before it is written to disk. To avoid
this risk, set this parameter to zero. If you use Write-
back Caching, we recommend that you back up your
system data regularly and, if possible, utilize a
uninterrupted power supply (UPS).
Write-through Caching— this is the same as Write-back
Caching except that the data is immediately transferred from
the cache to disk before sending the status to the host system.
The Write-through Caching setting defines the maximum
Write command size beyond which the write data will not be
cached at all but instead written immediately to disk. With
write-through cache the data is written to disk and also stored
in the cache. This enables faster I/O performance if the
application needs to read the data that was recently written.
The Write-through Caching setting must always be greater
than the Write-back Caching setting.
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