Exposing zfs snapshot to windows previous version using samba vfs_shadow_copy2

notes.md

Exposing zfs snapshot to windows previous version using samba vfs_shadow_copy2

This was much trickier than I had originally anticipated and have spent a few hours testing.

The config from samba wiki absolutely works, but it wasn't ranked higher in search engine and it's not general enough. https://github.com/zfsonlinux/zfs-auto-snapshot/wiki/Samba

Tested on ubuntu 22.04LTS, samba 4.15.9 and windows 11.

TLDR

If you snapshot utility labels the snapshot in a format other than [wildcard][timestmap], it's unlikely that it will work. sanoid and zfsnap both have dynamic labels after the timestamp, so they won't work.

Wildcard prefix

The default names for zfs-auto-snapshot is zfs-auto-snap_[label]_%Y-%m-%d-%H%M. This is the minimal viable config.

vfs_objects = shadow_copy2
shadow:snapdir = .zfs/snapshot
shadow:snapprefix = .*
shadow:delimiter = -20
shadow:format = -%Y-%m-%d-%H%M

Optional:

shadow:snapdirseverywhere = yes

Things that don't

Don't try to get creative, shadow_copy2 is extremely particular.

• -20 works as NULL for shadow:delimiter. I haven't found anything else that worked in its place. Dashes, hypens, regex patterns, alpha only strings, quoted, empty quotes, etc etc.
• removing the leading - from shadow:format.
• Using regex anywhere besides shadow:snapprefix
• Quoting your parameter

Examples that don't work

shadow:snapprefix = zfs-auto-snap_hourly
shadow:delimiter = -
shadow:format = %Y-%m-%d-%H%M

shadow:snapprefix = zfs-auto-snap
shadow:delimiter = _hourly-
shadow:format = %Y-%m-%d-%H%M

shadow:snapprefix = zfs-auto-snap_
shadow:delimiter = hourly
shadow:format = -%Y-%m-%d-%H%M

shadow:format = .*-%Y-%m-%d-%H%M

Examples that do work

The original config from samba wiki, but won't generalize for other snapshot naming pattern.

vfs objects = shadow_copy2
shadow:snapdir = .zfs/snapshot
shadow:format = -%Y-%m-%d-%H%M
shadow:snapprefix = ^zfs-auto-snap_\(frequent\)\{0,1\}\(hourly\)\{0,1\}\(daily\)\{0,1\}\(monthly\)\{0,1\}
shadow:delimiter = -20

If you don't need regex/wildcards, then using just hard code everything in shadow:format.

vfs objects = shadow_copy2
shadow: snapdir = .zfs/snapshot
shadow: sort = desc
shadow: format = zfs-auto-snap_hourly-%Y-%m-%d-%H%M

Other notes

• sanoid uses : in the snapshot names, vfs objects = catia and some extra catia config is needed for the folders under the hidden .zfs to display properly.
• Using some of the shadow options will force you to specify another option. For example: snapprefix and snapdir. Read the manpage carefully.
• The zfs-auto-snapshot package from ubuntu installs cron jobs in /etc/cron.d, /etc/cron.hourly, and etc.

• contrary to what one would assume, delimiter isn't actually used a delimiter between snapprefix and format in the source code (!!!)

So true, that freaked me out as well! See the PS in my comment from 2021 ;-) jimsalterjrs/sanoid#5 (comment)

I spent too much time trying to make it work myself and with LLMs.

At the end, was just feeding the LLM with configs and logs, hoping at least those could understand what's wrong.

Finally, I fed my configs to LLMs alongside with those notes, and it just gave me the fix on the first try.

Thanks, man!