ZFS root File System

[Pawel Jakub Dawidek]

On Fri, Feb 27, 2009 at 07:21:15PM -0800, Matthew Dillon wrote:
>     My experience with one of our people trying to do the same thing 
>     w/ HAMMER... we got it working, but it is not necessarily cleaner.
> 
>     I'd rather just boot from a small UFS /boot partition on 'a' (256M
>     or 512M), followed by swap on 'b', followed by the big-ass root
>     partition on 'd' using your favorite filesystem.

That's what I do on almost all of my company's servers. Except for...

>     The boot code already pretty much handles this state of affairs, one only
>     needs:
> 
>     (1) To partition it this way.
> 
>     (2) Add line to /boot/loader.conf pointing the kernel at the actual root,
> 	e.g. (in my case):
> 
> 	vfs.root.mountfrom="hammer:ad6s1d"

This is not needed if you have etc/fstab with this one entry on your
boot partition.

>     (3) Adjust sysctl kern.bootfile in e.g. /etc/sysctl.conf.  Since the
> 	boot loader thinks the kernel is on / instead of /boot (because
> 	/boot is the root from the point of view of the bootloader),
> 	it might set this to "/kernel" instead of "/boot/kernel".  So
> 	you may have to override it to make crash dumps and name lists
> 	work properly.

This is also not needed. My boot partition has boot/ and etc/
directories and I mount it under /bootdir.
Then I create symlink /boot -> bootdir/boot.

>     (4) Add a mount for the little /boot partition in /etc/fstab.
> 
>     Trying to create one large root on 'a' puts the default spot for swap
>     on 'b' at the end of the disk instead of near the beginning.  The end
>     of the disk (closer to the spindle) is a bad place for swap.  Having
>     a small /boot partition there instead retains the ordering and puts the
>     swap where it is expected to be.
> 
>     # df
>     Filesystem         1K-blocks     Used     Avail Capacity  Mounted on
>     /dev/ad6s1d        193888256  1662976 192225280     1%    /
>     /dev/ad6s1a           257998   110896    126464    47%    /boot
> 
>     --
> 
>     In anycase, if RAID is an issue the loader could always be adjusted to
>     look for a boot partition on multiple disks.  One could then have a /boot
>     on two independant disks, or even operate it as a soft-raid-mirror.  It
>     seems less of an issue these days since someone with that sort of
>     requirement who isn't already net-booting can just pop in a SSD for
>     booting which will have approximately the same or better MTBF as the
>     motherboard electronics.

My 'a' (boot) and 'b' (swap) partitions are mirrored using gmirror.

For example:

	puppet:root:~# mount -t ufs,zfs
	system/root on / (zfs, local, noatime)
	/dev/mirror/boot on /bootdir (ufs, local, noatime)
	system/jails on /jails (zfs, local, noatime)
	system/tmp on /tmp (zfs, local, noatime, nosuid)
	system/usr on /usr (zfs, local, noatime)
	system/home on /usr/home (zfs, local, noatime, nosuid)
	system/home/pjd on /usr/home/pjd (zfs, local, noatime, nosuid)
	system/usr/obj on /usr/obj (zfs, local, noatime)
	system/usr/ports on /usr/ports (zfs, local, noatime)
	system/usr/ports/distfiles on /usr/ports/distfiles (zfs, local, noatime)
	system/usr/share on /usr/share (zfs, local, noatime)
	system/usr/src on /usr/src (zfs, local, noatime)
	system/var/log on /var/log (zfs, local, noatime)
	system/var/tmp on /var/tmp (zfs, local, noatime, nosuid)
	puppet:root:~# swapctl -l
	Device:			1024-blocks	Used:
	/dev/mirror/swap.eli	4194300		0

Some file systems like /tmp, /usr/src, /usr/ports, /usr/share, /var/log
and /var/tmp are compressed.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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