ZFS: Is 'zpool add' really irreversible?

Brandon J. Wandersee brandon.wandersee at gmail.com
Mon Jun 13 00:55:05 UTC 2016

Yuri writes:

> People may reasonably want to remove some disks in some layouts, due
> to failures, etc, and ZFS just lacks the flexibility to do that.

Obviously, if you're dealing with any sort of RAID you'll occasionally
be replacing failed disks; ZFS is no different, and you can swap out
disks while the system is running. You just can't remove a *virtual
device*. You can't just shuffle disks around willy-nilly, because you'd
effectively destroy the storage pool in the process. There's a minimum
number of disks that need to be attached, and that minimum changes as
you add virtual (not necessarily physical) devices to a
pool. Traditional RAID has the same sort of limitation: create a RAID 5
array out of three disks, then remove two disks. You've just destroyed
the array.

If you want to temporarily add a single disk to a system, you can just
create a second pool on it. There's no arbitrary limit to how many pools
a system can have. ZFS has real limitations, but they're not that strict.


::  Brandon J. Wandersee
::  brandon.wandersee at gmail.com
::  --------------------------------------------------
::  'The best design is as little design as possible.'
::  --- Dieter Rams ----------------------------------

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