gmirror, geli, gjournal performance
ivoras at freebsd.org
Sat Apr 19 21:27:13 UTC 2008
> Hi everyone,
> I was replacing a disk in a gmirror+geli pair and decided to compare
> the performance of gmirror+geli+gjournal before adding the new disk.
> When using these three together is the appropriate order to 1) fdisk
> and label 2) mirror the disk, 3) geli the partitions, and 4) use the
> geli partitions for gjournal label?
It depends on what you want to do. To minimize administration overhead
I'd modify the sequence like this: gmirror the drives, geli the entire
gmirror, then fdisk it, then add gjournal, use UFS labels. Of course,
you can never boot from such a thing.
> With respect to performance, I find the writes to the gjournal disk
> about half as fast, which I expected from the benchmarks I've seen.
> However, reading a single file is identical between the two:
> dd if=/sofupdates/1.mpg of=/dev/null bs=1m
> 994049168 bytes transferred in 34.858793 secs (28516454 bytes/sec)
> dd if=/gjournal/1.mpg of=/dev/null bs=1m
> 994049168 bytes transferred in 34.335267 secs (28951258 bytes/sec)
> Is this expected? I was under the impression that reads should be
> somewhat faster with gjournal. Is geli decryption the limiting
> factor here?
No, performance with gjournal can at most be as fast as without gjournal
(in reality it will always be infinitesimally slower since there's
another layer in GEOM added).
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