From: Jeff Lightner (jlightner@water.com)
Date: Wed Nov 02 2005 - 14:25:00 EST
We have a couple of filesystem that had 10 x 512 MB Oracle redo logs on
each. We added space to the filesystems and the DBAs then expanded the
10 redo logs from 512 MB to 1 GB each. They are now complaining about
performance of the redo logs and claim it has to do with filesystem
fragmentation.
They claim the last time they did something similar (256 MB to 512 MB)
that they had the admin copy the files out (with the DB down of course)
then newfs the filesystem and copy the files back in to get rid of the
fragmentation.
Since we have OnlineJFS this seemed unnecessary to me and sure enough on
reading and perusing forums found info on doing fsadm -ed for defrag.
(-e for extent level and -d for directory level).
As a test I used a separate filesystem and did prealloc to create 10 x
512 MB files. I then did a remove of the first file and did prealloc to
1 GB then a remove of the second file and a prealloc to 1 GB etc...
until all 10 had been done. This all to simulate the fragmentation.
Running ncheck and sorting/grepping for different information I was able
to see the different extent ranges in use for each of the files. I also
ran fsadm -ED to see the extent/directory fragmentation. On doing the
fsadm -ed though I saw some but not a lot of improvement in
fragmentation. On read of the man page I saw comments about maximum
extent size allowed for move being modified with -l. Since default was
64 and max was 2048 I tried the fsadm -ed -l 2048 to see if it helped
but it didn't.
However when I did the copy out to another filesystem then did a newfs
on the original and copied back in sure enough ncheck showed a much
better defragmentation. It appears therefore the fsadm defrag isn't of
much use (at least for my 1 GB files).
So am I missing something or is it just that the fsadm defrag really has
no value for this purpose?
Note: Please don't suggest "-F vxfs" as vxfs is in /etc/default/fs and
per the man page that is the fstype it assume if -F isn't specified.
Jeffrey C. Lightner
Unix Systems Administrator
DS Waters of North America
678-486-3516
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