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Message-ID: <20051230185840.52264.qmail@web34113.mail.mud.yahoo.com>
Date: Fri, 30 Dec 2005 10:58:40 -0800 (PST)
From: Kenny Simpson <theonetruekenny@yahoo.com>
Subject: Re: RAID controller safety
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: linux kernel <linux-kernel@vger.kernel.org>
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--- Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> On Gwe, 2005-12-30 at 08:18 -0800, Kenny Simpson wrote:
> > That's what I read in the comments too, but looking at the code I only ever see it set to
> > write-back.  I verified this with blktool - our controllers have no battery, and blktool
> showed
> > the i2o-wcache state as write-back.
> 
> blktool doesn't support i2o control as far as I am aware. The blk level
> generic ioctls are just too crude to control it properly.

>From man blktool dated August 2004:
       i2o-wcache
              Query or set an I2O block device's write cache.

> 
> > However, I was also told that the i2o_block driver lacks barrier support, so even in the
> > write-back case, the controller won't be told to flush/sync.
> 
> Correct, but it should only ever enable this in the battery backed case.
> Otherwise it uses the per command control bits to decide what mode it
> wishes to use for each I/O

So all writes would be treated as syncronous in the write-through case (no battery), making fsync
a no-op?

-Kenny


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