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Re: cache+barriers vs cache+nobarriers vs disabled cache+barriers vs dis

To: Leon Kolchinsky <leonk@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: cache+barriers vs cache+nobarriers vs disabled cache+barriers vs disabled cache+nobarriers
From: Chris Wedgwood <cw@xxxxxxxx>
Date: Sun, 18 Mar 2007 14:33:13 -0700
Cc: "'Martin Steigerwald'" <Martin@xxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: <20070318101304.BAA2E193E9@mail.edu.haifa.ac.il>
References: <200703151339.36259.Martin@lichtvoll.de> <20070318101304.BAA2E193E9@mail.edu.haifa.ac.il>
Sender: xfs-bounce@xxxxxxxxxxx
On Sun, Mar 18, 2007 at 12:07:11PM +0200, Leon Kolchinsky wrote:

> My goal is to avoid filesystem corruption at any cost

doing what?  applications can still lose data if they're not careful

> (while trying to use fastest FS for linux) and according to the FAQ
> disabling write cache is the right way to do it.

unless you applications are care, it's typical that reliability is
going to cost in terms of performance

> Power/Hardware failure may occur in-between the flushes (with write
> barrier enabled) so the safe way (I think) is to disable write
> cache.

i've heard (but nobody has been able to give conrete details on this)
that disabling the write-cache on modern drives will lessen their
lifespan, often considerably

with write barriers sane applications should be just as safe as when
you disable the write cache

> It's interesting if there is a significant drop in the performance
> with disabled disk "write cache" and XFS filesystem comparing to
> ext3+enabled "write cache".

that's expected, w/o the write-cache drives are typically a lot slower
for many loads (why else would they put a write cache in disks afetr

> Has anyone some statistics or tests comparing ext3+enabled write
> cache vs.  xfs+disabled write cache?

why would you compare those two?  why ext3 w/ caches enabled and xfs
w/ caches disabled?

anyhow, it depends on your load, for some loads ext3 is faster and
others xfs is faster

what access patterns are you expecting?

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