continuous backup solution for FreeBSD

[Matthew Dillon]

:> boot2/loader does not speak ZFS -- this is why you need the /boot UFS2
:> partition.  This is an annoyance.
:> 
:> For the final "stage/step", vfs.root.mountfrom="zfs:mypool/root" in
:> loader.conf will cause FreeBSD to mount the root filesystem from ZFS.
:> This works fine.
:
:so the answer is:
:	yes, if you have only one disk.
:	no, if you have ZFS over many disks
:
:because I see no advantage in the springboard solution where ZFS is used to
:cover several disks.
:
:I'm asking, because I want to deploy some zfs fileservers soon, and so
:far the solution is either PXE boot, or keep one disk UFS (or boot off a USB)
:Today's /(root+usr) is somewhere between .5 to 1Gb(kernel+debug+src),
:and is readonly, so having 1 disk UFS seems to be a pitty.
:
:danny

    I think it is is perfectly acceptable to have a /boot + ZFS style
    solution, where /boot is a small ~256M UFS filesystem that the
    system actually boots from (containing only the kernel, modules,
    loader.conf, etc), and ZFS is the root filesystem.  In a running
    system /boot would be mounted under the ZFS root.

    All I needed was a line in /boot/loader.conf to tell the kernel
    where the root FS was.  In my case, I pointed it at HAMMER.

	vfs.root.mountfrom="hammer:ad0s1d"

    This gives you the flexibility of being able to have as complex a
    root FS as you want.

Filesystem                      1K-blocks    Used    Avail Capacity  Mounted on
HAMMER_ROOT      36388864 9789440 26599424    27%    /
/dev/ad0s1a        257998  100074   137286    42%    /boot
/pfs/@@-1:00001  36388864 9789440 26599424    27%    /usr
/pfs/@@-1:00003  36388864 9789440 26599424    27%    /var
/pfs/@@-1:00006  36388864 9789440 26599424    27%    /tmp
/pfs/@@-1:00007  36388864 9789440 26599424    27%    /home
/pfs/@@-1:00005  36388864 9789440 26599424    27%    /var/tmp
/pfs/@@-1:00002  36388864 9789440 26599424    27%    /usr/obj
/pfs/@@-1:00004  36388864 9789440 26599424    27%    /var/crash
procfs                  4       4        0   100%    /proc

     The /boot is small enough that it can be dealt with numerous ways,
     including simple duplication if you have multiple disks (have a
     adXs1a on two drives).  And if you were really that worried you
     could put /boot on a SSD.  Frankly, anything that has approximately
     the same MTBF as the motherboard itself is suitable, there's really
     no point trying to make /boot disk-redundant when the motherboard
     and memory aren't redundant.  If you have more then one HD connected
     to the system, and you want boot redundancy, then you also likely
     have the $$ to purchase a tiny SSD for your /boot.

     The big problem trying to boot from a completely generic FS setup
     is that it tends to severely limit your options.  You might want to
     have more flexibility in your root filesystem that you could otherwise
     accomodate if /boot were integrated into it.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>