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Re: howto keep xfs directory searches fast for a long time

To: xfs@xxxxxxxxxxx, stan@xxxxxxxxxxxxxxxxx, Peter Grandi <pg_xf2@xxxxxxxxxxxxxxxxxx>
Subject: Re: howto keep xfs directory searches fast for a long time
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 13 Aug 2012 18:44:34 +0200
In-reply-to: <5028057F.3090007@xxxxxxxxxxxxxxxxx>
Organization: it-management http://it-management.at
References: <6344220.LKveJofnHA@saturn> <5028057F.3090007@xxxxxxxxxxxxxxxxx>
User-agent: KMail/4.7.2 (Linux/3.5.1-zmi; KDE/4.7.2; x86_64; ; )
First, thanks to both of you.

Am Sonntag, 12. August 2012, 14:35:27 schrieb Stan Hoeppner:
> So the problem here is max vmdk size?  Just use an RDM.

That would have been an option before someone created the VDMK space
over the full RAID ;-)

> Peter Grandi:
> Ah the usual goal of a single large storage pool for cheap.

I don't need O_PONIES or 5.000 IOPS. I've just been trying to figure out
if there's anything I can do to "optimize" a given VM and storage space
via xfs formatting. This I guess is what 95% of admins worldwide have to
do these days: Generic, virtualized environments with a given storage,
and customer wants X. Where X is sometimes a DB, sometimes a file store,
sometimes archive store. And customer expects endless IOPS, sub-zero
delay, and endless disk space. I tend to destroy their ponies quickly,
but that doesn't mean you can't try to keep systems quick.

That particular VM is not important, but I want to keep user
satisfaction at a quality level. About 10 times a week someone connects
to that machine, searches a file and downloads it over the Internet. So
download or read speed is of no value. But access/find times are.

I guess the best I can do is run du/find every morning to pre-fill the
inode caches on that VM, so when someone connects the search runs fast.

The current VM shows this:

# df -i /disks/big1/
Filesystem                    Inodes   IUsed      IFree IUse% Mounted on
/dev/mapper/sp1--sha 1717934464 1255882 1716678582    1% /disks/big1
# df /disks/big1/
Filesystem               1K-blocks       Used  Available Use% Mounted on
/dev/mapper/sp1--sha 8587585536 6004421384 2583164152  70% /disks/big1

So 6TB data in 1.3 mio inodes. The VM caches that easily, seems that's
the only real thing to optimize against.

http://xfs.org/index.php/XFS_FAQ#Q:_I_want_to_tune_my_XFS_filesystems_for_.3Csomething.3E

CFQ seems bad, but there's no documented way out of that. I've edited
that, and added a short vm.vfs_cache_pressure description. Please
someone recheck.

--
mit freundlichen Grüssen,
Michael Monnerie, Ing. BSc

it-management Internet Services: Protéger
http://proteger.at [gesprochen: Prot-e-schee]
Tel: +43 660 / 415 6531

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