Back in the beginning of last year we disabled mode page 8 and mode page
3f requests through device quirk bits instead of enhancing the driver to
respond to these mode pages because there was no apparent added value.
The Firmware that supports the new communication commands supports the
ability to force a write around of the adapter cache on a command by
command basis. In the attached patch we enable mode page 8 and 3f and
spoof the results as needed in order to *convince* the layers above to
submit writes with the FUA (Force Unit Attention) bit set if the file
system or application requires it, if the Firmware supports the write
through, or instead to submit a SYNCHRONIZE_CACHE if the Firmware does
not. The added value here is for file systems that benefit from this
functionality and for clustering or redundancy scenarios.
Caveats: By convince, we are responding with a minimal short 3 byte
content mode page 8, with only the data the SCSI layer needs and that we
can fill confidently. Applications that require the customarily larger
mode page 8 results may be confused by this(?). The FUA, or the
SYNCHRONIZE_CACHE only affect the cache on the controller. Our firmware
by default ensure that the underlying physical drives of the array have
their cache turned off so normally this is not a problem.
This attached patch is against current scsi-misc-2.6 and was unit tested
on RHEL5. Since this is a feature enhancement, it should not be
considered for any current stabilization efforts.
Signed-off-by: Mark Salyzyn <aacraid@adaptec.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
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