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

To: Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Thu, 14 Apr 2011 11:14:59 -0500
Cc: Pádraig Brady <P@xxxxxxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, coreutils@xxxxxxx
In-reply-to: <20110414160343.GA12787@xxxxxxxxxxxxxx>
References: <20110414102608.GA1678@xxxxxxxxxxxxxx> <20110414120635.GB1678@xxxxxxxxxxxxxx> <20110414140222.GB1679@xxxxxxxxxxxxxx> <4DA70BD3.1070409@xxxxxxxxxxxxxx> <4DA717B2.3020305@xxxxxxxxxxx> <4DA7182B.8050409@xxxxxxxxxxxxxx> <4DA71920.9@xxxxxxxxxxx> <20110414160343.GA12787@xxxxxxxxxxxxxx>
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On 4/14/11 11:03 AM, Markus Trippelsdorf wrote:
> On 2011.04.14 at 10:56 -0500, Eric Sandeen wrote:

...

>> well, if I simply take the preallocation step out of the testcase, it works 
>> fine on xfs without a sync.
>>
>> So I still don't know what Markus hit...
> 
> Maybe it's delalloc:
> 
> x4 /tmp # dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k       
>                                                                         
> 10+0 records in
> 10+0 records out
> 5120 bytes (5.1 kB) copied, 0.0021822 s, 2.3 MB/s
> x4 /tmp # filefrag -v k 
> Filesystem type is: 58465342
> File size of k is 5120 (2 blocks, blocksize 4096)
>  ext logical physical expected length flags
>    0       0        0              16 unknown,delalloc,eof
> k: 1 extent found
> x4 /tmp # sync
> x4 /tmp # filefrag -v k 
> Filesystem type is: 58465342
> File size of k is 5120 (2 blocks, blocksize 4096)
>  ext logical physical expected length flags
>    0       0 26960045              16 eof
> k: 1 extent found
> 

well filefrag still returns that it knows of a valid range from logical blocks 
0 to 16, so cp should have something to copy...

-Eric

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