How to Access Trapped Dataset Snapshot?

[NASbox]

I'm hoping that someone who has some experience with snapshots can help me.

I have saved a number of snapshots of datasets from pool TANK using zfs send/receive to a removable pool BACKUP01.
(TANK has grown too large for a single backup volume, so I need to back it up in pieces.)

Code:

NAME													  USED  AVAIL  REFER  MOUNTPOINT
BACKUP01												 6.23T   816G	88K  /BACKUP01
BACKUP01/TANK											6.23T   816G   230G  /BACKUP01/TANK
BACKUP01/TANK@__BKP01_VJQRCPRG_20171229_143300			111M	  -   230G  -
BACKUP01/TANK@__BKP01_VJQRCPRG__20180421_224503			  0	  -   230G  -
[Deleted for clarity]
BACKUP01/TANK/video									   836G   816G   836G  /BACKUP01/TANK/video
BACKUP01/TANK/video@__BKP01_VJQRCPRG_20171229_143300	  208K	  -   818G  -
BACKUP01/TANK/video@__BKP01_VJQRCPRG__20180421_224503		0	  -   836G  -

My problem is that the parent dataset TANK (which as expected contains none of the child datasets) is preventing me from accessing any of the child datasets that I have backed up.

For example if I try to access /BACKUP01/TANK/video it points to an empty directory in the parent dataset instead of the 836G of data that was backed up as a separate snapshot.

What is the best way to access the copy of BACKUP01/TANK/video that contains the data instead of the empty one.

Also if anyone has seen any good articles/videos that explain the finer points of handling snapshots of pools/child pools it would be much appreciated.
I've figured out how to save the data, now I have to figure out how I'm going to restore it if TANK ever gets corrupted.

Any hints/advice/assistance is much appreciated.

 

[sretalla]

You are going to want to mount the snapshot in order to see the content it holds:

Code:

mount -t zfs BACKUP01/TANK/video@__BKP01_VJQRCPRG_20171229_143300 /mnt/videobackup

Assumes you have created the dir /mnt/videobackup first.

Credit to dpearcefl:
https://forums.freenas.org/index.php?threads/access-to-the-files-from-a-snapshot.36472/

*** Edited to correct the command ***

 

[NASbox]

You are going to want to mount the snapshot in order to see the content it holds:

Code:

mnt -t zfs BACKUP01/TANK/video@__BKP01_VJQRCPRG_20171229_143300 /mnt/videobackup

Assumes you have created the dir /mnt/videobackup first.

Credit to dpearcefl:
https://forums.freenas.org/index.php?threads/access-to-the-files-from-a-snapshot.36472/

Thanks @sretalla that helped me figure things out.

For the benefit of noobs who may not know this should be:

Code:

mount -t zfs BACKUP01/TANK/video@__BKP01_VJQRCPRG_20171229_143300 /mnt/videobackup

Now for an interesting follow up:

I chose to create /media/snap and mount the snapshot to that directory. After taking a quick look, I unmounted with umount /media/snap
and automagically ALL the child datasets backed up on BACKUP01 (there were 4) mounted themselves to /BACKUP01/TANK under the appropriated directory (since the directory exists).

I'm not complaining, but is this expected behaviour?

EDIT:
Follow up:
Just because I could (pool is a single disk in a removable drive caddy), I exported BACKUP01, and then imported it again, and everything was mounted as expected.

It appears that doing zfs send TANK/video@(oldsnapname) zfs send TANK/video@(newsnapname) | zfs recv BACKUP01/TANK/video

either unmounts the datasets or messes up the mount (not sure which). Exporting and Importing the Pool solves the problem. No need to mount any snapshots unless I need an old snapshot.

I thought the group might find this helpful.