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Re: Premature "No Space left on device" on XFS

To: Bernhard Schmidt <berni@xxxxxxxxxxxxx>
Subject: Re: Premature "No Space left on device" on XFS
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Thu, 06 Oct 2011 19:22:08 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4E8E079B.4040103@xxxxxxxxxxxxx>
References: <4E8E079B.4040103@xxxxxxxxxxxxx>
Reply-to: stan@xxxxxxxxxxxxxxxxx
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:7.0.1) Gecko/20110929 Thunderbird/7.0.1
On 10/6/2011 2:55 PM, Bernhard Schmidt wrote:
> Hi,
> 
> this is an XFS-related summary of a problem report I sent to the postfix
> mailinglist a few minutes ago after a bulkmail test system blew up
> during a stress test.
> 
> We have a few MTAs running SLES11.1 amd64 (2.6.32.45-0.3-default), 10 GB
> XFS Spooldirectory with default blocksize (4k). It was bombarded with
> mails faster than it could send them on, which eventually led to almost
> 2 million files of ~1.5kB in one directory. Suddenly, this started to
> happen
> 
> lxmhs45:/var/spool/postfix-bulk/postfix-bulkinhss # touch a
> touch: cannot touch `a': No space left on device
> lxmhs45:/var/spool/postfix-bulk/postfix-bulkinhss # df .
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/sdb              10475520   7471160   3004360  72%
> /var/spool/postfix-bulk
> lxmhs45:/var/spool/postfix-bulk/postfix-bulkinhss # df -i .
> Filesystem            Inodes   IUsed   IFree IUse% Mounted on
> /dev/sdb             10485760 1742528 8743232   17% /var/spool/postfix-bulk
> 
> So we could not create any file in the spool directory anymore despite
> df claiming to have both free blocks and inodes. This led to a pretty
> spectacular lockup of the mail processing chain.
> 
> My theory is that XFS is using a full 4k block for each 1.5kB file,
> which accounts to some loss. But still, 10GB / 4kB makes 2.5 mio files,
> which have surely not been reached here. Is there that high overhead?
> Why is neither df-metric reporting this problem? Is there any way to get
> reasonable readings out of df in this case? The system would have
> stopped accepting mail from outside if the freespace would have sunk
> below 2GB, so out-of-space happened way to early for it.

Dig deeper so you can get past theory and find facts.  Do you see any
errors in dmseg?

-- 
Stan

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