On Sat, Oct 27, 2012 at 9:21 AM, Edward Ned Harvey
(opensolarisisdeadlongliveopensolaris) <
opensolarisisdeadlongliveopensola...@nedharvey.com> wrote:

> > From: Edward Ned Harvey (opensolarisisdeadlongliveopensolaris)
> >
> > Performance is much better if you use mirrors instead of raid.
>  (Sequential
> > performance is just as good either way, but sequential IO is unusual for
> most
> > use cases. Random IO is much better with mirrors, and that includes
> scrubs &
> > resilvers.)
> Even if you think you use sequential IO...  If you use snapshots...
>  Thanks to the nature of snapshot creation & deletion & the nature of COW,
> you probably don't have much sequential IO in your system, after a couple
> months of actual usage.  Some people use raidzN, but I always use mirrors.

This may be the case if you often rewrite portions of files, so especially
database usage, but if you generally write entire new files rather than
modifying old ones, I wouldn't expect fragmentation to be that bad.  The
particular workload I have is like this, if a file is changed, it is
overwritten entirely, so I went with raidz2 vdevs for more capacity.
However, I'm not exactly pushing the limits of the pool performance, as my
bottleneck is network.

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