Re: else or Debian (Re: ZFS performance (was: Re: deduplicating file systems: VDO with Debian?))
On Thu, 2022-11-10 at 23:12 -0500, Michael Stone wrote:
> On Thu, Nov 10, 2022 at 08:32:36PM -0500, Dan Ritter wrote:
> > * RAID 5 and 6 restoration incurs additional stress on the other
> > disks in the RAID which makes it more likely that one of them
> > will fail.
>
> I believe that's mostly apocryphal; I haven't seen science backing that
> up, and it hasn't been my experience either.
Maybe it's a myth that comes about when someone rebuilds a RAID and yet another
disk in it fails (because they're all same age and have been running under same
conditions). It's easy to jump to conclusions and easy jumps is what people
like.
OTOH, it's not too unplausible that a disk might fail just when it's working
particularly hard. If it hadn't been working so hard, maybe it would have
failed later because it had more time to wear out or when the ambient
temperatures are higher in the summer. So who knows?
> > The advantage of RAID 6 is that it can then recover
> > from that...
>
> The advantage to RAID 6 is that it can tolerate a double disk failure.
> With RAID 1 you need 3x your effective capacity to achieve that and even
> though storage has gotten cheaper, it hasn't gotten that cheap. (e.g.,
> an 8 disk RAID 6 has the same fault tolerance as an 18 disk RAID 1 of
> equivalent capacity, ignoring pointless quibbling over probabilities.)
so with RAID6, 3x8 is 18 instead of 24
With 18 disks more can go wrong than with 8. That's all kinda confusing.
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