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Re: ENOSPC at 90% with plenty of inodes

To: xfs@xxxxxxxxxxx
Subject: Re: ENOSPC at 90% with plenty of inodes
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Mon, 11 Oct 2010 20:27:00 -0500
In-reply-to: <20101011223507.GB32255@dastard>
References: <AANLkTinwnOm0V=9WwbXiUGFnyjCwT3GUHo0hiQahQNUV@xxxxxxxxxxxxxx> <20101008225146.GJ4681@dastard> <AANLkTikLyEuSoFRVwirKLws97Vemz4ScNHOqu2Jc5sWR@xxxxxxxxxxxxxx> <20101011223507.GB32255@dastard>
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Dave Chinner put forth on 10/11/2010 5:35 PM:
> On Mon, Oct 11, 2010 at 03:03:28PM +0100, James Braid wrote:
>> On Fri, Oct 8, 2010 at 23:51, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>>> Sounds like fragmented free space. What is the output of:
>>>
>>> # xfs_db -r -c "freesp -s" <device>
>>
>> # xfs_db -r -c "freesp -s" /dev/sdb
>>    from      to extents  blocks    pct
>>       1       1 2298052 2298052  40.52
>>       2       3 1568338 3337017  58.84
>>       4       7    8432   35716   0.63
>>       8      15      50     423   0.01
>> total free extents 3874872
>> total free blocks 5671208
>> average free extent size 1.46359
>>
>> Which seems to say there are a few tiny pieces of free space
>> available? The files that were failing to be written were a few
>> hundred bytes in size.
> 
> The error has nothing to do with the size of the files, but
> everything to do with being able to allocate more inodes. Inode
> allocation requires 4 contiguous blocks (for 256 byte inodes, more
> for larger inodes) with alignment constraints. That means when you
> run out of 8 block or larger free extents, inode allocation will
> start failing and you'll get ENOSPC being reported.
> 
>> We haven't seen any errors so far today, but xfs_fsr ran over the
>> weekend, so perhaps I guess it's reorganized the filesystem.
> 
> Only a little. xfs_fsr will not improve fragmented free space
> conditions (indeed, it normally fragments free space more). The only
> way to reduce the fragmentation of free space is to remove a
> significant amount of data and inodes from the filesystem...

Hay Dave, would a "backup/reformat/restore" help with free space
fragmentation in this case?  If so, could/should the OP specify anything
during the mkfs.xfs reformat that may help alleviate or mitigate his
problem in the future?

-- 
Stan

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