How much space does raidz2 'eat'?

[Matthew Seaman]

On 24/11/2014 07:16, Matthew Seaman wrote:
> On 23/11/2014 22:26, Christian Baer wrote:
>> After creating a raidz2 pool, I get this:
> 
>> Now I know that while WD works with kB, FreeBSD works with KiB (factor
>> 1024). However, if I break this drive down to that and multiply that by
>> 5, I get 18.19TiB, while df gives me 16TiB. Sure, there is some
>> overhead and all, but certainly (hopefully) not 2 whole TiB! That would
>> be more than 10%.
> 
> Use 'zpool list' to see the actual size and usage of your pool.
> 
> The amount you lose in overhead from partitioning and setting up geli
> providers is pretty neglible; it's all down

(oops.  missed a bit)

... in the noise with the TB scale drives you're using.

> Yes, RAIDZ2 has around that level of overhead: think two parity blocks
> for each three data blocks, so worst case is that about 40% of your raw
> space will disappear.  The actual amount depends on exactly how many
> drives you're using.
> 
>> Is this normal or am I missing something?
> 
> See: http://blog.delphix.com/matt/2014/06/06/zfs-stripe-width/
> 
> 	Cheers,
> 
> 	Matthew
> 


-- 
Dr Matthew J Seaman MA, D.Phil.

PGP: http://www.infracaninophile.co.uk/pgpkey
JID: matthew at infracaninophile.co.uk

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