[Lustre-discuss] fseeks on lustre

[Andreas Dilger]

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.