[Lustre-discuss] Random access is not improving

Cliff White Cliff.White at Sun.COM
Mon Apr 6 11:14:21 PDT 2009


sethpn at gmail.com wrote:
> Does Lustre increase random access performance?  I would like to know
> this becauseI have a large random access file (a hash table).  I have
> striped this file across multiple OSTs.  The file is 24 gigabytes, and
> the stripe size was 1gig across 10 OSTs.  I also tried a stripe size
> of 100megabytes.  Both stripe sizes did not seem to improve random
> access performance.  Am I doing something wrong?
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I may be wrong, but I would think performance of a single random access
would still be mostly limited by disk seek times, etc.

Lustre should do better with multiple random queries, since they should 
be spread across multiple disk spindles. Less chance of two queries 
contending for the same spindle.

But there is nothing we do that will make a single disk access any 
faster, afaik. If you are jumping about randomly, it's going to be up to 
the disk heads.

Changing the stripe size won't do anything here. If you are doing 
multiple random queries, increasing the number of OSTs would spread the 
load out.

This is a case where a future feature (OST cache) might help.

cliffw



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