[Lustre-discuss] fseeks on lustre

[Ronald K Long]

We are doing SEEK_SET

fseek(fp,offset[i],SEEK_SET

We were running into this same issue on our san file system until we set 
the dma_cache_read_ahead to match our buffer size of 256k.  Just wondering 
if there is away to set that within lustre.  We are running 1.8 on the MDS 
and OSS and the clients running the fseek are are running 1.6

Thanks again.



Rocky



From:
Andreas Dilger <andreas.dilger at oracle.com>
To:
Ronald K Long <rklong at usgs.gov>
Cc:
lustre-discuss at lists.lustre.org
Date:
04/09/2010 10:52 AM
Subject:
Re: [Lustre-discuss] fseeks on lustre



On 2010-04-07, at 14:09, Ronald K Long wrote:
> I am having an issue with our lustre file system.  In our current 
> environment on a san file system opening a large file and doing 
> fseeks completes in under 2 seconds.  Running that same routine on 
> our lustre file system the routine actually never finishes.

Doing fseek() itself is only a client-side operation, so it should 
have no performance impact, UNLESS you are doing SEEK_END, which 
requires that the actual file size be computed on the client.  That 
causes lock revocation from all of the clients and is an expensive 
operation.  Using SEEK_CUR or SEEK_SET has no cost at all.

> Are there any tunable parameter in lustre that can alleviate this 
> problem?

It depends on what the problem really is.

Cheers, Andreas
--
Andreas Dilger
Principal Engineer, Lustre Group
Oracle Corporation Canada Inc.



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