simple zfs query

[krad]

On 24 March 2010 11:33, Matthew Seaman <m.seaman at infracaninophile.co.uk>wrote:

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> On 24/03/2010 10:31:51, John wrote:
> > With ZFS and 3x 2Tb SATA disks, what percentage of theoretical diskspace
> > would I realise? I'm hoping at least 5Tb would be usable?
>
> That depends on how you configure your zpool.  The choices are:
>
>  disk -- just uses the disk directly as a vdev.  Means you can use 100%
>         of the space, but you have absolutely no resilience
>
>  mirror -- for which you'ld need an even number of disks and you get 50%
>           of the raw as usable space.  Can survive at least one disk
>           failure, and possibly up to as many as half of the disks
>           failing.
>
>  raidz -- single parity (equivalent to RAID5).  For N disks, 1 disk
>          worth is used for parity data, leaving N - 1 disks' worth as
>          the actual capacity. So you'ld get 66% of raw in your case.
>          Can survive failure of any one disk.
>
>  raidz2 -- double parity (equivalent to RAID6). For N disks, 2 disks
>           worth are used for parity data, leaving N - 2 disks worth as
>           actual capacity. Or 33% of raw in your case.  Can survive
>           failure of any two disks.
>
> Note that 3 drives is the minimum for either of the raidz types, and
> won't give you the best performance.  See zpool(1M) for details.
>
>        Cheers,
>
>        Matthew
>
> - --
> Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
>                                                  Flat 3
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If you want 100% of the drives you could have a pool per drive. Its not as
nice as one big pool, but its less risky than one big raid0