On Tue, 24 Apr 2012, "Trent W. Buck" <trentbuck@gmail.com> wrote:
BTW, this is hidden from ext users, because the default "5% reserved for root user" is not shown in df, and is used as the "wiggle room". If you set it to 0%, or wilfully and repeatedly fill the fs as root, the fragmentation of the ext fs in question rapidly rises from 2% to (say) 75%.
Which generally doesn't cause problems. I've got a lot of systems that had "tune2fs -m0" run on them and I've never seen any serious performance problems as a result. I don't recall seeing any ext[34] system have a performance problem when almost full that it didn't have when ~75% full. Certainly nothing like the timeout problems referred to earlier in this thread. It probably helps that the most write-intensive systems I run are mail servers which have an average file size of something less than 100KB which leaves less possibility of file fragmentation. I think that one reason for this is that an almost full ZFS/BTRFS system will suddenly start getting serious fragmentation of writes which would otherwise be contiguous. While for Ext[23] and other non-COW filesystems you get writes all over the place for metadata anyway so it doesn't change things as much. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/