waiting for root device: could be duplicate UUIDs

If you run into waiting for root device when booting in verbose mode or you get a flashing question mark, etc, it could be that your volumes have duplicate UUIDs. The UUID is the primary means that is used to locate the boot volume to root from. If you have duplicate UUIDs, your Mac may not be able to determine which volume to boot from. If you suspect this may be the case, boot from another disk or CD and run diskutil list to get a list of all volumes. Then run diskutil info on each to get the UUIDs. Check for duplicates.

kserver:~ pbuffer$ diskutil list
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *74.5 Gi disk0
1: EFI 200.0 Mi disk0s1
2: Apple_HFS int_1 19.8 Gi disk0s2
3: Apple_HFS int_2 19.8 Gi disk0s3
4: Apple_HFS int_3 34.5 Gi disk0s4

kserver:~ pbuffer $ diskutil info disk0s2 | grep UUID
Volume UUID: A1F5866F-8286-359A-B19F-58910918AC5A
kserver:~ pbuffer$ diskutil info disk0s3 | grep UUID
Volume UUID: A1F5866F-8286-359A-B19F-58910918AC5A
kserver:~ pbuffer $ diskutil info disk0s4 | grep UUID
Volume UUID: CBB0B1F8-07D5-3BFC-9B50-4F99033B01D6

If you do find a duplicate, you can generate a new UUID and set it using the following command:

unmount the disk first

diskutil unmountDisk disk0

/System/Library/Filesystems/hfs.fs/hfs.util -s disk0s2

substitute your own device for disk0s2

Once you’ve done this, re-bless the volume.

Duplicate UUIDs shouldn’t happen, but somehow it happened to one of our Xserves with a hardware raid card.

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Leopard’s bless command references to ZFS?

The bless command in Leopard contains references to ZFS.

kserver:~ pbuffr$ strings /usr/sbin/bless | grep -i zfs
No ZFS container partitions found
ZFS container partition found: %s

Since bless is the command that sets the boot variables in nvram to set your a startup volume, it seems likely that Apple is at least working on boot support for ZFS, if it isn’t already there, but hidden away.¬†¬†Interesting.¬†