gmirror, geli, gjournal performance

[Ivan Voras]

hideo wrote:
> 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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