zfs discuss - Dec 2009 - L2ARC re-uses new device if it is in the same "place"

Hi,


milek at r600:/rpool/tmp# zpool status test
  pool: test
 state: ONLINE
 scrub: none requested
config:

    NAME             STATE     READ WRITE CKSUM
    test             ONLINE       0     0     0
      /rpool/tmp/f1  ONLINE       0     0     0

errors: No known data errors

lets add a cache device:

milek at r600:/rpool/tmp# zfs create -V 100m rpool/tmp/ssd2
milek at r600:/rpool/tmp# zpool add test cache /dev/zvol/dsk/rpool/tmp/ssd2
milek at r600:/rpool/tmp# zpool status test
  pool: test
 state: ONLINE
 scrub: none requested
config:

    NAME                            STATE     READ WRITE CKSUM
    test                            ONLINE       0     0     0
      /rpool/tmp/f1                 ONLINE       0     0     0
    cache
      /dev/zvol/dsk/rpool/tmp/ssd2  ONLINE       0     0     0

errors: No known data errors
milek at r600:/rpool/tmp#

now lets export the pool, re-create the zvol and then import the pool again:
> milek at r600:/rpool/tmp# zpool export test
> milek at r600:/rpool/tmp# zfs destroy rpool/tmp/ssd2
> milek at r600:/rpool/tmp# zfs create -V 100m rpool/tmp/ssd2
> milek at r600:/rpool/tmp# zpool import -d /rpool/tmp/ test
milek at r600:/rpool/tmp# zpool status test
  pool: test
 state: ONLINE
 scrub: none requested
config:

    NAME                            STATE     READ WRITE CKSUM
    test                            ONLINE       0     0     0
      /rpool/tmp/f1                 ONLINE       0     0     0
    cache
      /dev/zvol/dsk/rpool/tmp/ssd2  ONLINE       0     0     0

errors: No known data errors
milek at r600:/rpool/tmp#


No complaint here...
I''m not entirely sure that it should behave that way - in some 
circumstances it could be risky.
For example what if zvol/ssd/disk which is used on one server as a cache 
device has the same path on another server and then a pool is imported 
there? Would l2arc just blindly start using it as a cache device and 
overwriting some other data?

Shouldn''t l2arc devices have a label/signature or at least use uuid of
a
disk and during import be checked if it is the same device? Or maybe it 
does and there is some other issue here with re-creating zvol...

btw: x86, snv_127

-- 
Robert Milkowski
http://milek.blogspot.com