Background:
- I use lvm snapshots on ext4 for backup. I use dump to backup the
snapshots. The backup goes to an external hard drive over usb 3.0. The
external hard drive has 1 partition formatted with ext4.
Problem:
- I've noticed the performance of dump to my ext4 backup degrades
linearly as the disk fills. In the output, the kbps in the status line
keeps getting lower as the percent complete keeps getting higher.
My Thoughts So Far:
- I suspect that either 1) dump is doing something which lowers
performance as the backup progresses, or 2) the ext4 algorithm for
finding and allocating free blocks is vulnerable to performance
degradation as the volume fills.
- I haven't tested this thoroughly. However, performance appears to
improve when I clear out the external drive and do a fresh, full dump
(-0), and performance appears to remain degraded on incremental backups
on a nearly full volume. This leads me to suspect #2.
Help from you:
- What steps can I take to isolate the cause of the problem? If there's
any information I can provide, please let me know.
What I've Done:
- I've run both the short and long SMART tests on the external drive,
which came back clean. They also told me the relocated sector count was
zero.
- I also made sure the disk was connecting in usb 3.0 mode.
- I changed the external drive ext4 mount from journal=ordered to
journal=writeback. The performance difference was nominal.
Any insight would be appreciated.
Thanks.
Joseph D. Wagner
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
