TIME-MACHINE(7)        Miscellaneous Information Manual        TIME-MACHINE(7)

NAME
     Time Machine – an awful one

DESCRIPTION
     If, like me, you have a Raspberry Pi 3 at home that you've just upgraded
     to FreeBSD 13.0 which has a hard drive from an old laptop attached to it
     by USB adapter with ZFS on it and you want to use that as a Time Machine
     backup destination over SMB using samba(8), despite samba(8) being awful
     software and using ZFS on a system with only 1 GB of RAM being a terrible
     idea, this is how to do it.

     In /usr/local/etc/smb4.conf:

           [global]
           vfs objects = zfsacl catia fruit streams_xattr
           fruit:metadata = stream
           fruit:model = Macmini

           [TimeMachine]
           read only = no
           path = /media/zhdd/backup/TimeMachine
           fruit:time machine = yes
           fruit:time machine max size = 250G

     The important thing here is zfsacl in the vfs objects list.  Most pages
     will tell you about the others, but without zfsacl Time Machine will just
     fail to create the backup and not provide any useful error.  I'm not
     actually sure if the fruit:metadata setting is required, but a bunch of
     pages recommend it.  The fruit:model just makes it look nice in Finder.
     The rest creates an SMB share called “TimeMachine” that macOS will be
     willing to use.  You can limit the size of the share that samba(8)
     reports so that Time Machine doesn't fill up the whole drive.

     The other important thing to do is to create some swap space.  When I
     first tried backing up to this share, it stopped after a while because
     smbd(8) got killed when there was nowhere to swap pages to.  A wiki page
     told me to create swap on ZFS like this:

           zfs create -V 2G \
                   -o org.freebsd:swap=on \
                   -o checksum=off \
                   -o compression=off \
                   -o dedup=off \
                   -o sync=disabled \
                   -o primarycache=none \
                   zhdd/swap
           swapon /dev/zvol/zhdd/swap

     To be fair to samba(8), most of the memory is being used by the ZFS ARC
     (which you can see in top(1)), but smbd(8) still seems to be using far
     more memory than is reasonable.  It's interesting seeing processes with 0
     RES in htop(1) because they're all being swapped out while the ARC takes
     half the available RAM.  And having to wait for my shell to be paged back
     in when I quit htop(1).

     Anyway, as expected this whole thing is terribly slow.  On my initial
     backup, I'm currently at 26.49 GB of 104.22 GB with an estimate of 8
     hours remaining.  Normally transfer time estimates are wildly inaccurate,
     but I think in this case it's right.

AUTHORS
     june <june@causal.agency>

BUGS
     FreeBSD doesn't seem to want to mount the ZFS volumes on the hard-drive-
     over-USB automatically at boot.  I have to zpool-import(8) the drive
     manually each time.  I don't know if there's a workaround for this, but I
     don't have anything essential to the system on the drive, and it doesn't
     need to reboot often.

Causal Agency                   April 25, 2021                   Causal Agency