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Re: XFS and write barriers.

To: linux-xfs@xxxxxxxxxxx
Subject: Re: XFS and write barriers.
From: Martin Steigerwald <Martin@xxxxxxxxxxxx>
Date: Thu, 29 Mar 2007 16:56:21 +0200
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Am Montag 26 März 2007 schrieb David Chinner:

> > Is there some mount flag to say "cope without barriers" or "require
> > barriers" ??
>
> XFs has "-o nobarrier" to say don't use barriers, and this is
> *not* the default. If barriers don't work, we drop back to "-o
> nobarrier" after leaving a loud warning inthe log....

Hello David!

Just a thought, maybe it shouldn't do that automatically, but require the 
sysadmin to explicitely state "-o nobarrier" in that case. Safest default 
behavior IMHO would be either not to mount at all without "-o nobarrier" 
if the device has no barrier support or disable the write cache of that 
device. The latter can be considered a layering violation in itself.

BTW XFS copes really well here with commodity hardware such as my 
ThinkPads with 2.5 inch notebook harddisks *since* 2.6.17.7.

But right now I wondered about barrier support on USB connected devices? I 
have to check whether XFS does barriers on those. Does the usb mass 
storage driver support barriers?

Regards,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7


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