To refer to your original discussion, how were you writing your 1TB
file? I'm mainly wondering about the blocksize of the individual writes.
Marty Barnaby
Lundgren, Andrew wrote:
I get it.
Thanks!
-----Original Message-----
From: Kumaran Rajaram [mailto:[EMAIL PROTECTED]
Sent: Friday, May 30, 2008 3:07 PM
To: Lundgren, Andrew
Cc: Roger Spellman; [email protected]
Subject: RE: [Lustre-discuss] Performance Drop creating big files
I meant use file-size that are 4x the RAM size :-). So if
your RAM size
is 4GB, use atleast 16GB file-sizes for the benchmarks.
On Fri, 2008-05-30 at 15:03 -0600, Lundgren, Andrew wrote:
Are you suggesting he use machines with 40G of RAM to work
with 10G files?
We have many 800-900G files... I am not sure that is a
realistic number.
--
Andrew
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Kumaran Rajaram
Sent: Friday, May 30, 2008 3:01 PM
To: Roger Spellman
Cc: [email protected]
Subject: Re: [Lustre-discuss] Performance Drop creating big files
Roger,
I would suspect the Lustre client side caching
influencing your write
performance. 10GB is not adequate, try atleast 4x of the
RAM size for
file-sizes. Try doing the same tests with O_DIRECT flag
as it'd truly
measure your disk I/O performance bypassing FS + buffer cache.
HTH,
-Kums
On Fri, 2008-05-30 at 16:25 -0400, Roger Spellman wrote:
I am seeing the following odd behavior. I have several
OSSes, each
with a 7T RAID 5.
If I use a single client to create a single 1T file
which is striped
to a single OST, the performance starts off at about
400 MB/s (which
is typical for my HW), then gradually decreases, until it
reaches 250
MB/s. I've seen this with both IOZone and dd.
As an experiment, I wrote a script that creates two hundred
10G files,
without removing them. Again, the performance starts off
at 400 MB/s.
But, the performance stays nearly the same throughout the test.
The only difference between these tests is that in the
second case,
there are lots of opens & closes, and in the first case,
just a single
open and close.
Can anyone explain what is happening here, and how to
possible fix it?
Thanks.
Roger Spellman
Sr. Staff Engineer
Terascala, Inc.
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