Hello all, I'd like to report a tricky situation and a workaround I've found useful - hope this helps someone in similar situations.
To cut the long story short, I could not properly mount some datasets from a readonly pool, which had a non-"legacy" mountpoint attribute value set, but the mountpoint was not available (directory absent or not empty). In this case I could neither create/cleanup the mountpoints, nor change the dataset properties to mountpoint=legacy. After a while I managed to override a higher-level point in the FS tree by mounting tmpfs over it, and in that tmpfs I could make the mountpoints needed by zfs. I don't want to claim this adventure as a bug (because in this case zfs actually works as documented), but rather as an inconvenience that might need some improvement, i.e. to allow (forced?) use of "mount -F zfs" even for datasets with the mountpoint property defined. Here goes the detailed version: I was evacuating data from a corrupted rpool which I could only import read-only while booted from a LiveUSB. As I wrote previously, I could not use "zfs send" (bug now submitted to Illumos tracker), so I reverted to directly mounting datasets and copying data off them into another location (into a similar dataset hierarchy on my data pool), i.e.: # zpool import -R /POOL pool # zpool import -R /RPOOL -o readonly=on rpool My last-used root fs (rpool/ROOT/openindiana-1) had the property mountpoint=/ set, so it got mounted into /RPOOL of the LiveUSB environment. I copied my data off it, roughly like this: # cd /RPOOL && ( find . -xdev -depth -print | \ cpio -pvdm /POOL/rpool-backup/openindiana-1 ; \ rsync -avPHK ./ /POOL/rpool-backup/openindiana-1/ ) Likewise for many other filesystems, like those with legacy mountpoints (mounted wherever I like, like /mnt/1) or those with existing valid mountpoints (like /export). However I ran into trouble with secondary (older) root FSes which I wanted to keep for posterity. For whatever reason, the "mountpoint" property was set to "/mnt". This directory was not empty, and I found no way to pass "-O" flag to mount for ZFS automounted FSes (to mount over non-empty dirs). On a read-only rpool I couldn't clean up the "/mnt" dir. I could not use the "mount -F zfs" command because dataset's mountpoint was defined and not "legacy". I could not change it to legacy - because rpool is read-only. If I unmounted the "rpool/ROOT/openindiana-1" dataset, there was no "/mnt" left at all and no way to create one on a read-only pool. So I thought of tmpfs - I can mount these with "-O" anywhere and need no resources for that. First I tried mounting tmpfs over /RPOOL/mnt with "openindiana-1" mounted, but I couldn't mount the older root over this mountpoint directly. So I unmounted all datasets of "rpool", keeping the pool imported, and mounted tmpfs over the pool's alternate mount point. Now I could do my trick: # mount -F tmpfs -O - /RPOOL # mkdir /RPOOL/mnt # zfs mount rpool/ROOT/openindiana To be complete for those who might need this walkthrough, since I wanted to retain the benefits of root dataset cloning, I did that with my backup as well: # zfs snapshot pool/rpool-backup/openindiana-1@20110501 # zfs clone pool/rpool-backup/openindiana-1@20110501 \ zfs clone pool/rpool-backup/openindiana # cd /RPOOL/mnt && rsync -avPHK --delete-after \ ./ /POOL/rpool-backup/openindiana/ Thanks to rsync, I got only differing (older) files written onto that copy, with newer files removed. "cpio" and "rsync" both barked on some unreadable files (I/O errors) which I believe were in the zfs blocks with mismatching checksums, initially leading to the useless rpool. I replaced these files with those on the LiveUSB in the copy on "pool". Finally I exported and recreated rpool on the same device, and manually repopulated the zpool properties (failmode, bootfs) as well as initial values of zfs properties that I wanted (copies=2, dedup=off, compression=off). Then I used installgrub to ensure that the new rpool is bootable. I also set the zfs properties I wanted (i.e. copies=2, also canmount, mountpoint, caiman.* and others set by OpenIndiana, compression=on where allowed - on non-root datasets) on the rpool hierarchy copy in pool. Even though the actual data on "pool" was written with copies=1, the property value copies=2 will be copied and applied during "zfs send|zfs recv". Now I could "zfs send" the hierarchical replication stream from my copy in "pool" to the new "rpool", kind of like this: # zfs snapshot -r pool/rpool-backup@20111119-05 # zfs send -R pool/rpool-backup@20111119-05 | zfs recv -vF rpool Since the hardware was all the same, there was little else to do. I revised "RPOOL/rpool/boot/grub/menu.lst" and "RPOOL/etc/vfstab" just in case, but otherwise was ready to reboot. Luckily for me, the system came up as expected. That kind of joy does not always happen as planned, especially when you're half-a-globe away from the computer you're repairing ;) Good luck and strong patience to those in similar situations, //Jim Klimov _______________________________________________ zfs-discuss mailing list firstname.lastname@example.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss