[Bug 42939] hv_storvsc - write cache enabled by default and cannot be disabled

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https://bugzilla.kernel.org/show_bug.cgi?id=42939





--- Comment #1 from Mark <bugzilla-kernel-org-sux2k0@mstier.de>  2012-03-19 19:33:29 ---
Additional information:

trying to disable the writecache leads to the partition on the SCSI device
getting remounted read-only due to device errors.

Additional information (2):

I get 5.000 to 6.000 random reads per second even when manually creating the
fiometer file using random data from /dev/urandom (ie. fio doesn't access
zeroes in that case).

Additional information (3):

The host doesn't seem to cache anything: "dd iflag=direct if=/dev/sda bs=1M
of=/dev/null count=10" always and repeatedly gives me around 30-60 MB/s.

Additional information (4):

I did a simple MySQL InnoDB ACID transaction test where subsequent transactions
are done via a remote mysql client as fast as possible. I crashed the host
hardware and checked if all transactions reported as completed had been
committed to disk: no obvious problems there -- seemingly the reported
writecache has no writecache-effects at all...??

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