On Fri, Oct 07, 2011 at 06:58:53AM -0700, Bryan J Smith wrote: > [ Not really adding any technical meat, but just some past > experience with XFS, plus Ext3 experience ] > > I remember running into this a long time ago when I was first > playing with XFS for /tmp and /var (I was still a Linux/XFS noob > at the time, not that I'm an expert today). I ran into the same > case where both free block and inodes were still available > (although similarly well utilized), and the median file size was > around 1KiB. It was also in the case of many small files being > written out in a short period. > > In my case, I didn't use the XFS debugger to get into the > allocation of the extents (would have if I wasn't such a noob, > good, discrete command to know, thanx!). > > Extents are outstanding for data and similar directories, ordering > and placing large and small files to mitigate fragmentation. But > in this case, and correct me if I'm wrong, it's really just a > wasteful use for the extents approach, as the files typically fit > in a single data block or two. And single blocks still an extent, so there's nothing "wasted" by having a single block extent. .... > I've used Ext3 with around 8 million files with a median size well > under 4KiB (under 32GiB total). It works "well enough." I'm > curious how Ext4 would do though. I think Ric Wheeler's team (at > Red Hat) has done some benchmarks on 7+ figure file counts on Ext3 > and Ext4. And against XFS, too. In case you didn't realise, you're talking to the person who ran a large number of those tests. ;) The results were ext4 is good for create/delete workloads up to 2-4 threads and about 100k files per directory on a decent disk subsystem (4000 iops). It's much better than ext3, and for those workloads about 2x as fast as XFS at 1-2 threads. This pattern held true as long as the disk subsystem could handle the number of iops that ext4 threw at it. XFS performance came at a much, much lower iops cost (think order of magnitude), so shoul dbe more consistent on a wider range of storage hardware than ext4. However, XFS was about 3x faster on cold cache lookups than ext4, so if you're workload is dominated by lookups, XFS is definitely the faster filesystem to use even if creates/unlinks on ext4 are faster.. As soon as you have more parallelism than 2-4 threads or large directories, XFS create/unlink speed surpasses ext4 by a large amount - the best I got out of ext4 was ~80k creates a second, while XFS topped 130k creates/s at 8 threads. And the lookup speed differential increase in XFS's favour at larger thread counts as well. So it really depends on your workload as to which filesystem will handle your small files best. Mail spools tend to have lots of parallelism, which is why XFS works pretty well, even though it is a small file workload. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
