[Lustre-discuss] OSS Cache Size for read optimization

[Cliff White]

Jordan Mendler wrote:
> Hi all,
> 
> I deployed Lustre on some legacy hardware and as a result my (4) OSS's 
> each have 32GB of RAM. Our workflow is such that we are frequently 
> rereading the same 15GB indexes over and over again from Lustre (they 
> are striped across all OSS's) by all nodes on our cluster. As such, is 
> there any way to increase the amount of memory that either Lustre or the 
> Linux kernel uses to cache files read from disk by the OSS's? This would 
> allow much of the indexes to be served from memory on the OSS's rather 
> than disk.
> 
> I see a /lustre.memused_max = 48140176/ parameter, but not sure what 
> that does. If it matters, my setup is such that each of the 4 OSS's 
> serves 1 OST that consists of a software RAID10 across 4 SATA disks 
> internal to that OSS.
> 
> Any other suggestions for tuning for fast reads of large files would 
> also be greatly appreciated.
> 

Current Lustre does not cache on OSTs at all. All IO is direct.
Future Lustre releases will provide an OST cache.

For now, you can increase the amount of data cached on clients, which
might help a little. Client caching is set with 
/proc/fs/lustre/osc/*/max_dirty_mb.

cliffw

> Thanks so much,
> Jordan
> 
> 
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