[OpenIndiana-discuss] 800GB in 6 discs - 460GB in raidz

[Harry Putnam]

Timothy Coalson <tsc5yc at mst.edu> writes:

> On Fri, Mar 24, 2017 at 5:43 PM, Harry Putnam <reader at newsguy.com> wrote:
>>
>> On the vm, I've created discs like so:
>>
>> 2 @  96G
>> 2 @ 116G
>> 2 @ 216G
>>
>> These have just over 2x variation in size, and you put them all in a
> single raidz vdev, that is why your space is "missing" - it is just like
> making a mirror out of a 96G disk and a 216G disk, which would have only
> 96G available and "lose" over 100G of space.  raidz doesn't do anything
> magical for different-sized disks - it uses a slice from each device that
> is equal to the *smallest* device in the vdev.
>
> So, your raw space *before* parity or overhead (which is what "zpool list"
> says) should be 6*96G = 576G.  Remove 1 device worth for raidz1 (5*96G =
> 480G), and a fudge factor for metadata overhead, and lands you at the 460G
> that "zfs list" says about it.

Wow, I really have missed the boat here.  I did not realize that raidz
would reduce everthing to lowest common denominator.

I won't be so `tricky' with disc sizing from here on.  The sad part is
since it is vm stuff, I could of just as well used all 200G dics
and had 1200 g raw space ... or even better... 2 600g discs in
mirrored arrangement, and forget all about raidz.