Tuesday, December 11, 2007

Cat Proof External Storage

What happens when you disconnect the drive on the fly?
(e.g. set up a tripping hazard for your cat)

You get this message
The device you removed was not properly put away.Data might have been lost or damaged. Before youunplug your device, you must first select its icon inthe Finder and choose Eject from the File menu.
What happens when you do the same thing to a ZFS pool? This is no different
than what you get on Solaris, except it is on my Mac Book Pro.
  pool: p1
 state: DEGRADED
status: One or more devices could not be opened.  Sufficient replicas exist for
    the pool to continue functioning in a degraded state.
action: Attach the missing device and online it using 'zpool online'.
   see: http://www.sun.com/msg/ZFS-8000-D3
 scrub: scrub completed with 0 errors on Sat Dec  8 01:44:00 2007

    p1           DEGRADED     0     0     0
      mirror     DEGRADED     0     0     0
        disk7s1  UNAVAIL      0   114     0  cannot open
        disk0s3  ONLINE       0     0     0

Fortunately for me, my system keeps merrily chugging along.

Unfortunately (sort of) and this is much more of an issue on my Mac than on
any other system I am adding and removing devices much more frequently.

When I last connected the external disk and imported the pool I had 6
more "disks" visible to the system (really a usb thumb drive) another FW
device and a few SW RAID devices. This caused my nice portable external
FW disk to appear as disk7.
  diskutil list             
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *149.1 Gi   disk0
   1:                        EFI                         200.0 Mi   disk0s1
   2:                  Apple_HFS noroute                 88.9 Gi    disk0s2
   3:                  Apple_HFS                         57.0 Gi    disk0s3
   4:                  Apple_HFS noroute_2_1_2           2.6 Gi     disk0s4
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *55.9 Gi    disk1
   1:                  Apple_HFS                         55.9 Gi    disk1s1


The difference between the zpool status and diskutil list output
is the device configured for the pool is disk7s1 not the currently visible

I don't know how to recover from this situation live. If the device has not
renumbered you just zpool online p1 disk7s1 to reconnect on a different
device number I export and import the pool again.

To state that another way, I don't know how to effectively do:
zpool online p1
similar to
zpool replace p1
(the replace, even with -f, failed telling me that was busy)

I have just requested a pre-release tarball that is reported to fix some bugs
in the current beta. We will see how it goes.

Other Observations:

Once you load the RW kext, it appears that anyone can do anything to the ZFS pools
and filesystems. On my single user system this is OK. I am the only user and guest
accounts are disabled. e.g. Initiate a scrub as a non-admin guest account or create a
snpashot as nobody (sudo -u nobody zfs snapshot p1/Music@nobody)

You CANNOT download music from the iTunes store in the current beta. you get a
permission error. I can however add music from local files.


Edit: Cleaned up the block quotes a bit, still not really rendering as one might hope.

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