netbsd-5, i386, 2 x 400G SATA in rf RAID1, external USB2 WD Elements 1T I have a UFS2+WAPBL filesystem on the above RAID1 with ~900K files in ~320GB. I'm backing it up with rdiff-backup to a USB2 external disk. The external disk has a single large UFS2+WAPBL partition. I found that backups took crazy long -- as in most of a week -- when not that many of the files had changed. The rdiff-backup process was often in tstile or xscmd, but continue to apparently make progress. The disk busy % on both the RAID1 and external USB2 drive was only around 30%, but any use of disks was very very slow. If I suspended rdiff-backup, all seemed well, and I saw ~30 MB/s bulk read with dd and several hundred tps with du. With ktrace, I found that rdiff-backup seems to do fsync on every file, and each fsync takes most of a second. Other than that ktrace events happen in quick succession. With (yes, I know I'm living dangerously, and the machine is on a UPS): sysctl -w vfs.wapbl.flush_disk_cache=0 I am seeing about 11 transactions flushed per second (via sysctl -w vfs.wapbl.verbose_commit=1 ), and typically 300 tps and 3 MB/s on the USB2 disk. In 15 minutes the processed-file count has gone up 10K, vs 25K in about 4 hours. The previous backup of a smaller fs did 230K files in 18h. So things are still slow, but much better. I have run rdiff-backup from a remote machine (with host::/mnt/rdiff-backup/foo/bar as target), and that has seemed to be ok, processing a 300G filesystem (on which not much changes) in about an hour, via a 10 Mb/s network connection to a net5501 (lame USB) with a similar disk. I haven't looked yet, but it seems that rdiff-backup must not do fsync when using the ssh backend. So, I'm inclined to patch rdiff-backup not to fsync, since it seems excessive, and the backup is toast if the machine crashes before it is finished -- in that case rdiff-backup just rolls back. Opinions? I also wonder if we should have a vfs.wapbl.honor_fsync sysctl. But it seems the real issue here is fsync when there shouldn't be fsync, and such a sysctl seems a bit scary and otherwise unncessary.
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