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IDE write cache and journaling file systems

To: XFS List <linux-xfs@xxxxxxxxxxx>
Subject: IDE write cache and journaling file systems
From: Jim Buzbee <James.Buzbee@xxxxxxxxxxxx>
Date: Thu, 18 Apr 2002 09:28:24 -0600
Sender: owner-linux-xfs@xxxxxxxxxxx
We've got a bit of an issue. From conversations on this list over the
last few months, it appears as if enabling the write cache on an IDE
drive is a "bad thing" when using a journaling file system such as XFS. 
But, when talking to drive manufacturers, we are told that if the write
cache is disabled, the life of the drive is substantially reduced.  This
puts us in a bit of a hard place. We have little choice but to turn the
write cache on.  

In our application, (consumer set top box) we cannot always cleanly shut
down the system.  The consumer rightly expects to just unplug the box
when he wants/needs to.  I'm not terribly concerned about losing a bit
of data in such a case. I'm worried about file system corruption that
would turn the box into an expensive door stop. My own testing so far
has not shown any catastrophic failures, but if we have a million boxes
in the field, issues could start showing up.

The drive manufactures have recommended inserting IDE cache flushes at
critical sections of the code. I'm hesitant to muck with XFS internals,
and adding flushes in our user-space code would not cover all cases.

This has to be a common problem.  Does anyone have any strategies or
words of wisdom?

Jim Buzbee,
Echostar Technologies


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