deleting file takes longer than creating it

Stroller stroller at stellar.eclipse.co.uk
Wed May 5 08:55:05 CDT 2010


On 4 May 2010, at 23:25, John G. Heim wrote:

> I have  a Poweredge SE1435 which seems to be very slow and i noticed
> something odd... I can create a large file with dd faster than I can  
> delete
> it.
>
> # date; dd if=/dev/zero  of=zero.txt bs=1024 count=1000000; date; rm
> zero.txt; date
> Tue May  4 16:59:21 CDT 2010
> 1000000+0 records in
> 1000000+0 records out
> 1024000000 bytes (1.0 GB) copied, 11.7291 s, 87.3 MB/s
> Tue May  4 16:59:33 CDT 2010
> Tue May  4 17:00:09 CDT 2010
>
> It took 12 seconds to create the file and 33 seconds to rm it. Why  
> would
> that be?

Ou of curiosity, is there a reason you didn't do
  `time dd if=/dev/zero of=zero.txt bs=1024 count=1000000 && time rm  
zero.txt` ?

> This machine is serving as a print server, debian package mirror,  
> and a
> mmysql database server. I am not sure what kind of info you might  
> need to
> help me. But for starters, I'm running debian lenny with a 2.6.30  
> kernel.
> The file system is ext3.

I'm not saying this is wholly the reason, but ext3 is notoriously slow  
at deletions.

MythTV even had (has?) a special function to accommodate ext3,  
otherwise the deletion of a movie (which might well be several gigs in  
size) would lock the system solid for a minute or two, halting  
playback and corrupting any recordings in progress. See the  
"Filesystems" section at [1].

You may not be in a position to do this, but it would be interesting  
to upgrade the filesystem to ext4 with extents, then try again. I have  
found - only in typical use, no scientific testing - the delete  
performance between ext3 and ext4 to be *very* obvious.

Stroller.



[1] http://www.mythtv.org/docs/mythtv-HOWTO-3.html



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