On Fri, Mar 09, 2012 at 06:13:27PM -0800, Michael Spiegle wrote: > We're seeing some very strange behavior with XFS on the default kernel > for CentOS 5.6 (note, I have also 3.2.9 and witnessed the same issue). > The dataset on this server is about 1B small files (anywhere from 1KB > to 50KB). We first noticed it when creating files in a directory. A > simple 'touch' would take over 300ms on a completely idle system. If > I simply create a different directory, touching files is 1ms or > faster. Example: > > # time touch 0 > real 0m0.323s > user 0m0.000s > sys 0m0.323s > > # mkdir tmp2 > # time touch tmp2/0 > real 0m0.001s > user 0m0.000s > sys 0m0.000s Entirely normal. some operations require Io to complete (e.g. reading directory blocks to find where to insert the new entry), while adding the first file to a directory generally requires zero IO. You're seeing the difference between cold cache and hot cache performance. > We've done quite a bit of testing and debugging, and while we don't > have an answer yet, we've noticed that our filesystem was created with > the default of 32 AGs. When using xfs_db, we notice that all > allocations appear to be in AG0 only. Go look up what the inode32 and inode64 mount options do. The default is inode32.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
