> From: Cindy Swearingen [mailto:cindy.swearin...@oracle.com]
>
> I would not discount the performance issue...
>
> Depending on your workload, you might find that performance increases
> with ZFS on your hardware RAID in JBOD mode.
Depends on the raid card you're comparing to. I've certainly seen some raid
cards that were too dumb to read from 2 disks in a mirror simultaneously for
the sake of read performance enhancement. And many other similar
situations.
But I would not say that's generally true anymore. In the last several
years, all the hardware raid cards that I've bothered to test were able to
utilize all the hardware available. Just like ZFS.
There are performance differences... like ... the hardware raid might be
able to read 15% faster in raid5, while ZFS is able to write 15% faster in
raidz, and so forth. Differences that roughly balance each other out.
For example, here's one data point I can share (2 mirrors striped, results
normalized):
8 initial writers, 8 rewriters, 8 readers
ZFS 1.43 2.99 5.05
HW 2.00 2.54 2.96
8 re-readers, 8 reverse readers, 8 stride readers
ZFS 4.19 3.59 3.93
HW 3.02 2.80 2.90
8 random readers, 8 random mix, 8 random writers
ZFS 2.57 2.40 1.69
HW 1.99 1.70 1.73
average
ZFS 3.09
HW 2.40
There were some categories where ZFS was faster. Some where HW was faster.
On average, ZFS was faster, but they were all in the same ballpark, and the
results were highly dependent on specific details and tunables. AKA, not a
place you should explore, unless you have a highly specialized use case that
you wish to optimize.
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