linux-ext4 - Re: Mentor for a GSoC application wanted (Online ext2/3 filesystem checker)

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Message-ID: <480CDBFD.30009@redhat.com>
Date:	Mon, 21 Apr 2008 13:25:01 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	ric@....com
CC:	Andi Kleen <andi@...stfloor.org>, Theodore Tso <tytso@....edu>,
	Alexey Zaytsev <alexey.zaytsev@...il.com>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Rik van Riel <riel@...riel.com>
Subject: Re: Mentor for a GSoC application wanted (Online ext2/3 filesystem
 checker)

Ric Wheeler wrote:
> 
> Andi Kleen wrote:
>> On Mon, Apr 21, 2008 at 12:42:42AM +0100, Jamie Lokier wrote:
>>> Andi Kleen wrote:
>>>> [LVM] always disables barriers if you don't apply a so far unmerged
>>>> patch that enables them in some special circumstances (only single
>>>> backing device)
>>> (I continue to be surprised at the un-safety of Linux fsync)
>> Note barrier less does not necessarily always mean unsafe fsync,
>> it just often means that.
>>
>> Also surprisingly lot more syncs or write cache off tend to lower the MTBF 
>> of your disk significantly, so "unsafer" fsync might actually be more safe
>> for your unbackuped data.
>>
> 
> Hi Andi,
> 
> Where did you get this data?
> 
> I have never heard that using more barrier operations lowers the reliability or 
> the MTBF of a drive and I look at a fairly huge population when doing this ;-)

Ric, what about the other part - turning write cache off?  I've also
heard it suggested that this might hurt drive lifespan, and it sorta
makes sense, I assume it keeps the head working harder...

-Eric
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