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Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

To: xfs-oss <xfs@xxxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)
From: Pádraig Brady <P@xxxxxxxxxxxxxx>
Date: Thu, 14 Apr 2011 15:59:31 +0100
Cc: Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>, coreutils@xxxxxxx
In-reply-to: <20110414140222.GB1679@xxxxxxxxxxxxxx>
References: <20110414102608.GA1678@xxxxxxxxxxxxxx> <20110414120635.GB1678@xxxxxxxxxxxxxx> <20110414140222.GB1679@xxxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
On 14/04/11 15:02, Markus Trippelsdorf wrote:
>>> Hi Pádraig,
>>>
>>> here you go:
>>> + filefrag -v unwritten.withdata                                            
>>>                                                                          
>>> Filesystem type is: ef53                                                    
>>>                                                                          
>>> File size of unwritten.withdata is 5120 (2 blocks, blocksize 4096)          
>>>                                                                          
>>>  ext logical physical expected length flags                                 
>>>                                                                          
>>>    0       0   274432            2560 unwritten,eof                         
>>>                                                                          
>>> unwritten.withdata: 1 extent found
>>>
>>> Please notice that this also happens with ext4 on the same kernel. 
>>> Btrfs is fine.
>>
> `filefrag -vs` fixes the issue on both xfs and ext4.

So in summary, currently on (2.6.39-rc3), the following
will (usually?) report a single unwritten extent,
on both ext4 and xfs

  fallocate -l 10MiB -n k
  dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k
  filefrag -v k # grep for an extent without unwritten || fail

This particular issue has been discussed so far at:
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8411
Note there it was stated there that ext4 had this
fixed as of 2.6.39-rc1, so maybe there is something lurking?

cheers,
Pádraig.

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