Document Snapshot name requirements.

[ClashTheBunny]

I had a tough time figuring out why my snapshots would not transfer. The hint came when it printed a totally off the wall date of the unix epoch. Snapshot names must be formatted at dates. Old snapshots can be converted by listing the snapshots that aren't dates:
zfs list -r -t snapshot -o name,creation <volume> | grep -v "@[0-9]"
Followed by a zfs rename for each snapshot listed to the date listed converted to UTC:
zfs rename <volume>@backup-foo-2 2018-09-16-1200

A more robust way to do it would be if Perl's Date::Time(snapshot name) returns -1, we could treat the snapshot as if it were named the date of it's creation time locally and remotely. So we would have @backup-foo-2 locally and @2018-09-16-1200 remotely. That would let legacy snapshots transparently translate. It would always translate to the same thing, and it would never change (As long as the timezone was UTC?).

[jollyjinx]

Thanx for pointing out that problem of yours. Which ZFS version on which platforms are you using ?
If I change the format it will be iso8601 formatted, something like: 2018-09-17T07:20:02+02
but + is not allowed in snapshot names. so just 2018-09-17T07:20:02 using UTC should be ok.

[ClashTheBunny]

Sending
From:openzfs on osx v 1.7.2, El Cap. Perl 5.28, as the latest one segfaulted. Time::Date 2.30
To: Debian zfsonlinux 0.7.9-3.