Re: File System Performance

Lionel Bouton
2001-11-12T21:53:53Z

>
>
>
>I tried an experiment which puzzled me somwhat:
>
>> mount /xfs
>> cd /xfs/lord/xfs-linux
>> time tar cf /dev/null linux
>>
>
>real 0m7.743s
>user 0m0.510s
>sys 0m1.380s
>
>>hdparm -t /dev/sda5
>>
>
>/dev/sda5:
> Timing buffered disk reads: 64 MB in 3.76 seconds = 17.02 MB/sec
>
>>du -sk linux
>>
>173028 linux
>
>The tar got ~21 Mbytes/sec.
>
Things I'll check :

0/ rerun this test !!!
1/ is there cache on the scsi controler ?
2/ xfs data cached at mount ? (I don't believe so)
3/ "hdparm -t" is on crack.
4/ du reports a disk usage way ahead of files' sizes total (don't know
xfs enough to estimate this propability) and tar won't read the whole
"du -sk" data.

2/ "time mount /xfs" could help (if mount + tar times are below
expected, this case can be eliminated).
3/ ask hdparm's maintener.
4/ tar, check tar size.