The ufsdump block size doesn't seem to matter much

January 8, 2009

Some time ago I discovered that the Linux dump block size can make a significant performance difference. Ever since then I had in the back of my mind to find out if the same thing was true on other systems, with other versions of dump, and recently I got around to doing some experimentation on Solaris.

In the spirit of sharing negative results as well as positive ones: no, it doesn't seem to. I got a modest performance increase by specifying a b value greater than the default of 64 (32kb), with the best numbers seeming to happen around a b value of 256 (128 Kb). But at best this amounted to only a few megabytes a second, hardly the drastic improvements seen on Linux.

(The other way to look at the Linux numbers is to say that it performs terribly by default, while Solaris performs decently by default.)

Now, it's hard to be definitive about this (proving a negative is always challenging), since there could be any number of reasons that my testing had unusually slow results. However, I'm confidant enough that the results are applicable to real filesystems that I care about that I'm not going to bother with more testing.

(I did testing on both Solaris 8 SPARC and Solaris 10 x86 (64-bit), in both cases using filesystems on mirrored DiskSuite metadevices, and at least on the Solaris 10 system ufsdump's performance was well under the read speed of the raw metadevice.)

Written on 08 January 2009.
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Last modified: Thu Jan 8 02:20:24 2009
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