On Sep 6, 2009, at 11:19 AM, Al Lang wrote:
The "limitations" section of the Wikipedia article on ZFS currently
includes the statement:
"You cannot mix vdev types in a zpool. For example, if you had a
striped ZFS pool consisting of disks on a SAN, you cannot add the
local-disks as a mirrored vdev."
As I understand it, this is simply wrong. You can add any kind of
vdev to any zpool. Right?
This is so confusing that it makes absolutely no sense. I suspect the
author intended
to explain the limitation as described in the zpool(1m) man page:
Virtual devices cannot be nested, so a mirror or raidz vir-
tual device can only contain files or disks. Mirrors of mir-
rors (or other combinations) are not allowed.
so I edited it :-)
As I understand it, mixing vdev types is in general a bad idea. The
reliability of a zpool is dictated by its least reliable vdev and
the performance of a zpool tends to be limited by its lowest-
performing vdevs. So mixing vdev types tends to give you the worst
of all possible worlds.
It is really a data management issue, not a functionality issue. We
really do try to
help people not hurt themselves with complexity ;-)
-- richard
But this is merely a logical consequence of mixing storage types,
not anything to do with ZFS. Precisely analogous considerations
would apply when setting up RAID-10, for example.
Do I have that right?
Cheers,
Al.
--
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