dump(8) performance

Dan Nelson dnelson at allantgroup.com
Wed May 31 08:30:37 PDT 2006

In the last episode (May 31), Eugene M. Kim said:
> While watching the output of iostat -dxz -w10 -n100 to monitor the
> progress/performance of a dump(8) process straight to a tape, I found
> out something interesting and disappointing at the same time: The
> disk read throughput was exactly twice as high as the tape write
> throughput, throughout the entire dump phases 4 and 5, i.e. dumping
> actual inodes. Disappointing, because the tape drive utilization
> (%busy) was lingering around 35%-50% for most of the time; I didn't
> expect the disk would be the bottleneck. :p
> I want to believe that this indicates a bug in dump(8) which causes
> each disk block to be read twice, but being no UFS expert in any
> sense, I wonder: Could this behavior be by design, and would there be
> any room for improvement?

Are you using the -C option to dump?  I would expact that to help more
in the "dumping directories" step, but it might help later phases too.

	Dan Nelson
	dnelson at allantgroup.com

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