I'm setting up a new mail server, and am testing/tweaking IO. I have
two directories: /test/a which contains 750 mbox files totalling 8GB,
and /test/a2, which contains the exact same number of files, same names,
all zero length.
I am using ext3. I have done this experiment with both indexed and
non-indexed directories (mke2fs -O dir_index ...). I have also tried
setting the noatime mount option.
The times taken to do a directory listing are significantly different.
1037# time ls /test/a2 > /dev/null
real 0m0.006s
user 0m0.000s
sys 0m0.006s
1038# time ls /test/a > /dev/null
real 0m5.244s
user 0m4.875s
sys 0m0.346s
If I refer to a specific file, there's still a difference, but only 5x,
vs. 875x above.
1044# time ls a/anmbox > /dev/null
real 0m0.010s
user 0m0.009s
sys 0m0.002s
Fri Jun 10 10:31:02 root@slush:/db/tmp
1045# time ls a2/anmbox > /dev/null
real 0m0.002s
user 0m0.001s
sys 0m0.001s
I'm assuming this is normal behaviour. (?) However, I'd like to
understand what's happening a little better, and I'm wondering if
there's anything I'm overlooking vis-a-vis tuning my filesystem properly
for this type of application.
Linux 2.6.11.11 on Debian Sarge. Dell 2800 w/ LSI Megaraid on PCI/E to
Utra320 SCSI disks.
--
Ron Peterson
Network & Systems Manager
Mount Holyoke College
http://www.mtholyoke.edu/~rpeterso
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