ZFS – mounting corrupt zpools and datasets
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2 METHODS exist:

METHOD1 – mount the zpool readonly

METHOD2 – mount the zpool normal but without mounting any of the datasets/filesystems. then one by one mount each of the filesystems until you see the bad filesystem, then mount the bad filesystem with readonly flag set.

FIRST STEPS
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Get list of pools:
# zpool import

I see I have Vol1 and Vol2, each with datasets (cant see datasets yet, but we know they exist).

If this fails:

# zpool import Vol1
# zpool import Vol2

Each import also mounts the datasets (zfs filesystems) that are associated with each zpool.

Method1
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Try a readonly zpool import:

# zpool import -o readonly=on Vol1
# zpool import -o readonly=on Vol2

Now you can get your all of your data out.

Method2
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If that doesnt work you can zpool import just the zpool (without mounting the zfs filesystems/datasets), and then manually import/mount the zfs datasets – then when you find the bad dataset, just mount it readonly. Then you can backup the bad dataset and not have to backup EVERYTHING as in last step.

# zpool import -N Vol1

Then mount the datasets one by one

# zfs mount Vol1/Datasetname1
# zfs mount Vol1/Datasetname2
continue thru every data set

Then you will find out the bad dataset for example Datasetname2. So set the readonly flag on it

# zfs set readonly=on Vol1/Datasetname2

Now you can reboot the system should come up with those datasets as readonly. Do not copy out with “zfs send/zfs receive” as the corruption could creep over to the destination. Instead use cp -a, tar and tools like that to copy over.