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Re: zero size file after power failure with kernel

To: xfs@xxxxxxxxxxx
Subject: Re: zero size file after power failure with kernel
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Wed, 2 Sep 2009 00:52:41 +0200
In-reply-to: <19100.63566.98250.185404@xxxxxxxxxxxxxxxxxx>
Organization: it-management http://it-management.at
References: <200908292102.21710@xxxxxx> <200909010918.37886@xxxxxx> <19100.63566.98250.185404@xxxxxxxxxxxxxxxxxx>
User-agent: KMail/1.10.3 (Linux/; KDE/4.1.3; x86_64; ; )
On Dienstag 01 September 2009 Peter Grandi wrote:
> Other people have a very different impression. Like 'ext3'
> ReiserFS does ordered writes, but those don't necessarily help
> because of the colossal amount of buffering that happens anyhow
> nowadays.

Maybe. I had reiserfs on this system until two weeks ago, with this 
quad-core 8GB desktop. Had power failures, crashes, and so on. Can't 
remember a situation where a KDE app lost its config.

But I had a server with the OSS XEN, running a single VM which is my 
internal mailserver using PostgreSQL as it's store on XFS. My daughter 
managed to switch the server off (yeah, having redundant power supplies 
and UPS are still not enough). After reboot, the PostgreSQL database was 
*damaged*, so much that I had to restore. This should never have 
happened, and until now I don't know who was guilty for that: XFS? XEN? 
The RAID Controller with BBU and hard disk cache=off?
That's why I'm very sensible to even a small data loss (I had a backup 
of my kmail config), and I think the filesystem has to do everything to 
try to keep my data. XFS seems to be optimized more for speed before 
security, would you mean that? I've often heard "enterprise hardware", 
which sounds like "if anything crashes, it's your problem" ;-)

>   http://www.sabi.co.uk/blog/0707jul.html#070701

I like your blog, and
gave me a good hint to optimize tcp settings a long time ago.

> In general on a fast machine I would use:
>   vm/dirty_ratio                  =4
>   vm/dirty_background_ratio       =2
>   vm/dirty_expire_centisecs       =400
>   vm/dirty_writeback_centisecs    =200

Since May I use these new settings with kernel 2.6.(29|30):
vm.dirty_background_bytes = 16123456
vm.dirty_bytes = 250123456
vm.dirty_expire_centisecs = 1000
vm.dirty_writeback_centisecs = 100

(the expire was on 3000 until the crash).

mfg zmi
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