[Lustre-discuss] question about size on MDS (MDT) for lustre-1.8

Kit Westneat kwestneat at datadirectnet.com
Thu Jan 13 14:28:23 PST 2011

> It would probably be better to set:
> lctl conf_param fsname-OST00XX.ost.readcache_max_filesize=32M
> or similar, to limit the read cache to files 32MB in size or less (or whatever you consider "small" files at your site.  That allows the read cache for config files and such, while not thrashing the cache while accessing large files.
> We should probably change this to be the default, but at the time the read cache was introduced, we didn't know what should be considered a small vs. large file, and the amount of RAM and number of OSTs on an OSS, and the uses varies so much that it is difficult to pick a single correct value for this.
I was looking through the Linux vm settings and saw vfs_cache_pressure - 
has anyone tested performance with this parameter? Do you know if this 
would this have any effect on file caching vs. ext4 metadata caching?

For us, Linux/Lustre would ideally push out data before the metadata, as 
the performance penalty for doing 4k reads on the s2a far outweighs any 
benefits of data caching.


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