On 2012-07-06 14:00,
[hidden email] wrote:> It's easy to
find the failure math for raidz2 and raidz3.
>
> But what if you create a pool with 3 different raidz3 vdevs inside of
it ?
>
> For instance, 3 12-drive raidz3 vdevs in one big pool.
>
> For each individual vdev the failure probability is now higher, since
not only will it fail when 4 drives in the vdev fail, but it will also
fail if four drives in any of the other two vdevs fail.
>
> So each raidz3 vdev now has a failure rate higher than vanilla raidz3
... but what is that new failure rate ? Is it still higher than vanilla
raidz2 ?
Skip these calculations. They all assume that drive failures are
independent and it's not the case in the real world. There's been a good
study on the topic of drive failures several years ago,
http://static.usenix.org/events/fast07/tech/schroeder/schroeder_html/index.htmlAmong other findings they say:
"We also present strong evidence for the existence of correlations
between disk replacement interarrivals."
--
Twoje radio
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