On Thu, Nov 04, 2021 at 10:09:15AM +0100, Nikola Ciprich wrote: > Hello fellow XFS users and developers, > > we've stumbled upon strange problem which I think might be somewhere > in XFS code. > > we have very large ceph-based storage on top which there is 1.5PiB volume > with XFS filesystem. This contains very large (ie 500TB) sparse files, > partially filled with data. > > problem is, trying to read those files leads to processes blocked in D > state showing very very bad performance - ~200KiB/s, 50IOPS. It's been told it to go slow... :/ > I tried running xfs_repair on the volume, but this seems to behave in > very similar way - very quickly it gets into almost stalled state, without > almost any progress.. > > [root@spbstdnas ~]# xfs_repair -P -t 60 -v -v -v -v /dev/sdk .... because "-P" turns off prefetching and all the IO optimisation that comes along with the prefetching mechanisms. In effect, "-P" means "go really slowly". Try: # xfs_repair -o bhash_size=101371 -o ag_stride=100 /dev/sdk To get a good sized buffer cache and a decent (but not excessive) amount of concurrency in the scanning processing. It still may end up being slow if it has to single thread walk a huge btree (essentially pointer chasing on disk), but at least that won't hold up all the other scanning that isn't dependent on that huge btree.. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
