Arch Linux User Repository

In 2021, you probably don't want to use this. zrepl and sanoid are much better choices.

@xuanruiqi: That's good. Still, zfs-auto-snapshot-git is the first on the https://wiki.archlinux.org/index.php/ZFS#Automatic_snapshots list. You can pin your comment here, if you want. And I am very surprised that sanoid is not mentioned in the Wiki.

@willemw: I actually added the section about zrepl on the ZFS page in the Arch Wiki, since that's what I'm using.

@xuanruiqi: Maybe discuss or edit this on the main or discussion page of the ZFS Wiki?

Have switched to sanoid myself.

In 2021, you probably don't want to use this. zrepl and sanoid are much better choices.

the prefix_label_order patch was intended to make it easier to visually scan the snapshots when they are listed (as the datestamps are all aligned). And it also makes sorting simpler.

It is the case that it's incompatible with samba's vfs shadow copy2 "snapprefix" option. When the prefix_label_order change was added, snapprefix was not an option, and folks supported shadow copy with zfs-auto-snapshot by having the "daily"/"hourly"/etc label pretend to be seconds. See https://github.com/zfsonlinux/zfs-auto-snapshot/issues/10 for some solutions folks used.

It is somewhat unfortunate that zfs-auto-snapshot ever used the "daily"/"hourly"/etc labels on snapshots, as it's very feasible (via a bucketing algorithm) to avoid explicit tagging entirely. This is done, for example, in zrepl and snapper (no zfs support mainline in this one).

I've adopted this package because I recently moved from Btrfs to ZFS. I don't understand the point of the patch either. If anyone has any rationale for the patch, please enlighten me.

Disowned. Not using zfs-auto-snapshot anymore.

What is the real reason for the prefix_label_order.patch?

With this patch a snapshot name is like this: zpool@znap_2020-06-08-2200_daily Without the patch it should be like: zpool@znap_daily_2020-06-08-2200

But using the patched naming scheme breaks support for windows shadow copy in smb! So why there is the patch?

prefix_label_order.patch fails to apply after b0a5909. "Fixed" patch is below though it will need to be checked against the upstream changes to SNAPNAME and SNAPGLOB.

aurweb changes tabs to spaces (and trims trailing whitespace) so this won't work copy&paste. :( An actually-working version is here (for a week, anyway): https://bpaste.net/show/935b2a7beeba

diff --git a/src/zfs-auto-snapshot.sh b/src/zfs-auto-snapshot.sh
index 5ef5bae..75ba11d 100755
--- a/src/zfs-auto-snapshot.sh
+++ b/src/zfs-auto-snapshot.sh
@@ -398,9 +398,7 @@ if [ -n "$opt_fast_zfs_list" ]
 then
    SNAPSHOTS_OLD=$(env LC_ALL=C zfs list -H -t snapshot -o name -s name | \
        grep $opt_prefix | \
-       awk '{ print substr( $0, length($0) - 14, length($0) ) " " $0}' | \
-       sort -r -k1,1 -k2,2 | \
-       awk '{ print substr( $0, 17, length($0) )}') \
+       sort -t'@' -k2r,2 -k1,1) \
      || { print_log error "zfs list $?: $SNAPSHOTS_OLD"; exit 137; }
 else
         SNAPSHOTS_OLD=$(env LC_ALL=C zfs list -H -t snapshot -S creation -o name) \
@@ -569,10 +569,10 @@ SNAPPROP="-o com.sun:auto-snapshot-desc='$opt_event'"
 DATE=$(date --utc +%F-%H%M)

 # The snapshot name after the @ symbol.
-SNAPNAME="${opt_prefix:+$opt_prefix$opt_sep}${opt_label:+$opt_label}-$DATE"
+SNAPNAME="${opt_prefix}_$DATE${opt_label:+$opt_sep$opt_label}"

 # The expression for matching old snapshots.  -YYYY-MM-DD-HHMM
-SNAPGLOB="${opt_prefix:+$opt_prefix$opt_sep}${opt_label:+$opt_label}-???????????????"
+SNAPGLOB="${opt_prefix}????????????????${opt_label:+?$opt_label}"

 if [ -n "$opt_do_snapshots" ]
 then

Oh good, it looks like my comment did post properly this time. Basically the problem is that the zfs-auto-snapshot utility itself, when in --fast mode, uses some fairly hacky substring-sorting trickery to sort the snapshots by date, and that code was written based on the implicit assumption that the last component of the snap name will be the date+time. Here's my PKGBUILD diff that applies a patch to fix the sorting: https://gist.github.com/anonymous/b9772d6a1c89601435a0b6e44ac0e0cc (I've tested it with the 'PREFIX_DATE_LABEL' modification, but didn't check with the original 'PREFIX-LABEL_DATE' naming, so maybe check into that.)