[OpenIndiana-discuss] raidz2 as compared to 1:1 mirrors

[Judah Richardson]

With the exception of perhaps ReFS on Storage Spaces (due to the ability to
have multiple volumes with different redundancies in the same pool), all
CoW filesystem RAID schemes have the same basic *theoretical max* (note the
emphasis) storage calculation equation:

Usable storage, S = (N-p)C, where:

N = total number of disks
p = number of parity disks
C = (lowest) capacity per disk

So in your case, total theoretical max (read: actual value may be smaller
due to implementation details) = (8-2)*2 = 6*2 = 12 TB. The actual usable
space is lower <https://wintelguy.com/zfs-calc.pl> due to ZFS' reservations
(the implementation I mentioned earlier).

TL,DR: Yeah the results you're getting should be correct.

On Sun, Feb 21, 2021 at 4:10 PM reader <reader at newsguy.com> wrote:

> Tried to understand a couple of space calculators on line that are
> suppoded to show the rough space you end up with using the different
> zfs raid configs.
>
> I will have 8 2tb drives that I'd like to run in raidz2.
>
> My usual setup has always been 1 to 1 matching mirrored disks.
>
> So the loss in space that way is bit over 8TB or 50% and a bit more I
> think.
>
> If I understood the space calculator correctly it says I'll have
> nearly 11 tb usable out of the 16 raw.  That is quite a bit more
> space than 1:1 mirrors.
>
> Can anyone who actually uses raidz2 verify if the figures sound about
> right?
>
>
>
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