[Bug 13499] Write cache: disabled, read cache: enabled, supports DPO and FUA? it's bug???

[bugzilla-daemon@bugzilla.kernel.org]

http://bugzilla.kernel.org/show_bug.cgi?id=13499





--- Comment #2 from Anonymous Emailer <anonymous@kernel-bugs.osdl.org>  2009-06-10 14:14:13 ---
Reply-To: James.Bottomley@HansenPartnership.com

On Wed, 2009-06-10 at 14:00 +0000, bugzilla-daemon@bugzilla.kernel.org
wrote:
> why Write cache: disabled??

The SCSI mid layer is merely reporting what your array is telling it.
For arrays without a battery backed cache, write through configuration
(i.e. read cache enabled, write cache disabled) is the usual safe
default.

You can alter your write cache settings using Doug Gilbert's
sg3-utils ... but be warned, enabling the write cache without battery
backing in an array is a dangerous thing to do since most arrays have
huge caches, they either ignore SYNCHRONIZE CACHE (which would leave you
vulnerable to data loss on power failure) or take such a long time, it
would kill performance.

James

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