[CentOS] 6.2 kernel issues - followup

m.roth at 5-cent.us m.roth at 5-cent.us
Tue Mar 13 17:02:42 EDT 2012


I wrote:
> A couple weeks ago, after we moved a user's home directory from a 5.7
box to 6.2, he came
> to complain about slowness.

> Unpack file from NFS-mounted directory to local disk, like /tmp,
> everything's normal. cd to the NFS-mounted directory, and unpack it
there, and it was
> six to seven times slower. We repeated this a number of times, on a
number of machines. At
> first, we thought it was an NFSv4 issue, and I filed a bug with RedHat
about it.

> Then we did more testing; it seems to occur with 6.2; it's going to
happen if that's got ext4.

> However, my manager saw something else, just today: he noticed one of
our nightly backup
> servers was taking much, much longer to complete the rsync and delete.
Then he saw that I'd
> updated that backup server to 6.2, and after the backups started running
again (probably
> missing modules), they were taking a lot longer... about 6-7 times
longer. As in going from
> between .5 and 1 hr, to 5.5 to 9 hours.

Well, I was googling on performance tuning NFS, and found
<http://www.softpanorama.org/Net/Application_layer/NFS/nfs_performance_tuning.shtml>,
where the author notes "One issue with migrating to NFSv4 is that all of
the filesystems you export have to be located under a single top-level
exported directory. This means you have to change your /etc/exports file
and also use Linux bind mounts to mount the filesystems you wish to export
under your single top-level NFSv4 exported directory."

I makes a *real* difference. I tested it, on one 6.2 server, mounting a
foo directory I created in the usual 3 levels deep, and another,
/tmp/foo1, and doing my same unpack ran at 2/3rds the time. Not good - 6.5
min vs. 1+min for 5.7 & NFS3, but better.

This alone suggests we need to go back to NFS 3 - it would be a Big Deal
to relocate everyone's home directory.

Doing a yum list \*nfs\* shows something called sblim-cmpi-nfsv3.x86_64.
>From the info, I can't tell if I can just drop it in and run that, or if
I'd have to yum remove nfs-utils & nfs-utils-lib. Anyone have a clue?

         mark



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