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

[Jason Matthews]

11 TB is about right. Your 2TB disks will be "smaller" by nature of 
reporting differences. Much of that is difference between how drive 
manufacturers report a megabyte as 1,000,000 bytes and computers report 
a megabyte 1048576 bytes.

In a nutshell, in your raidz2 vdev you have eight drives. Two drives are 
for parity so you have six drives for data. 6*2 = 12TB less the 
accounting differences gives you 11TB and change.

This gives you space at the price of performance. You will have the 
write performance of roughly one disk and the read performance of six 
disks, excluding cache of course. That might be peachy for your 
application or it might not.  The best part is, you get to judge.

I almost never use raidz* if performance is a consideration.

j.

On 2/21/2021 2:10 PM, reader 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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