== ZFS GUIDs vs device names

One thing about [[ZFS GUIDs ZFSGuids]] that I didn't get around to
covering is when commands like '_zpool status_' are misleading you about
the device names that they show.

When things are fine, ie when ZFS can find the GUID that it is looking
for, the device name is correct (in fact hyper-correct, as '_zpool
status_' also checks that the device ID is the right one). When things
are not fine, _zpool_ will generally display the device name of the last
device that that GUID was found on; it does so even if the device name
doesn't actually exist on your system at the moment. (iSCSI devices are
good for this, since they can disappear if you sneeze on them.)

(Very recent versions of OpenSolaris will actually display the GUID and
then add 'most recently seen on <device>', which is the far more honest
and helpful approach. Apparently someone at Sun woke up.)

This usually doesn't matter for doing things to pool devices, because
_zpool_ will use the pool configuration to map device names to the GUIDs
it has to give the kernel. This is what lets you remove nonexistent
devices (or at least usually lets you remove them, there are some just
fixed ZFS bugs concerning removing nonexistent spares). If you have [[a
situation ZFSFaultedSpares]] where the same device name represents two
different GUIDs in the same pool, this breaks down but _zpool_ doesn't
seem to notice. (I think you usually get the GUID of the first instance
of the device name, which is usually the broken one.)