simple zfs query
kraduk at googlemail.com
Wed Mar 24 21:23:56 UTC 2010
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
> 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.
> - --
> Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
> Flat 3
> PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate
> Kent, CT11 9PW
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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
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