using existing legacy geom mirror disks with nas4free / freenas / later versions of BSD

I am in the process of retiring my old FreeBSD 5.5 based file server and replacing it with a more modern BSD distro that is aimed specifically at file serving duties. The setup of the current storage is all the disks are identical pairs and are configured using geom_mirror (RAID1) for redundancy. I'll be using a new motherboard and memory on the new server but will be re-using the existing disks. This got me to thinking if it would be a simple case of just plugging in the disks and having the new OS recognise them as containing GEOM metadata and thus allowing me to make use of them with minimal hassle?

I decided to prove or disprove this theory using my VMWare ESXi server.

Firstly, I created a FreeBSD 5.5 VM, and then a FreeBSD 9.0 VM. I decided to do it this way instead of using the actual NAS4Free distro as I know the NAS4Free distro is based upon FreeBSD9, so the end result should be the same!

I add two small extra disks to the 5.5 box and then go ahead and configure a RAID1 mirror:

$ su
Password:
bsd55# uname -a
FreeBSD bsd55 5.5-RELEASE FreeBSD 5.5-RELEASE #0: Tue May 23 14:58:27 UTC 2006     root@perseus.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386
bsd55# kldload /boot/kernel/geom_mirror.ko
bsd55# gmirror label gm055 da1 da2
bsd55# gmirror status
        Name    Status  Components
mirror/gm055  COMPLETE  da1
                        da2
bsd55# newfs /dev/mirror/gm055
/dev/mirror/gm055: 512.0MB (1048572 sectors) block size 16384, fragment size 2048
        using 4 cylinder groups of 128.00MB, 8192 blks, 16384 inodes.
super-block backups (for fsck -b #) at:
 160, 262304, 524448, 786592
bsd55# mount /dev/mirror/gm055 /mnt
bsd55# echo 'proof of conecpt' >/mnt/poc
bsd55# ls -l /mnt
total 4
drwxrwxr-x  2 root  operator  512 Aug 21 22:43 .snap
-rw-r--r--  1 root  wheel      17 Aug 21 22:49 poc
bsd55# cat /mnt/poc
proof of conecpt
bsd55# shutdown now
Shutdown NOW!
shutdown: [pid 574]
bsd55#                                                                          
*** FINAL System shutdown message from nf@bsd55 ***
System going down IMMEDIATELY



System shutdown time has arrived

Next I turn the power off on the 5.5 VM and then edit the settings for the 9.0 VM using vSphere client. What I am doing here is attaching the 5.5 mirrored disks to the 9.0 box:



Now I proceed to power on the 9.0 box and ssh into it to see what the new kernel makes of the old disks:

$ su
Password:
You have mail.
root@hg:/usr/home/nf # uname -a
FreeBSD hg 9.1-RELEASE FreeBSD 9.1-RELEASE #0 r243825: Tue Dec  4 09:23:10 UTC 2012     root@farrell.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64
root@hg:/usr/home/nf # kldload /boot/kernel/geom_mirror.ko
root@hg:/usr/home/nf # dmesg
GEOM_MIRROR: Upgrading metadata on da2 (v3->v4).
GEOM_MIRROR: Device mirror/gm055 launched (2/2).
GEOM_MIRROR: Upgrading metadata on da1 (v3->v4).
root@hg:/usr/home/nf # fsck -t ufs /dev/mirror/gm055
** /dev/mirror/gm055
** Last Mounted on /mnt
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
3 files, 3 used, 247891 free (27 frags, 30983 blocks, 0.0% fragmentation)

***** FILE SYSTEM MARKED CLEAN *****
root@hg:/usr/home/nf # mount /dev/mirror/gm055 /mnt
root@hg:/usr/home/nf # ls -l /mnt
total 4
drwxrwxr-x  2 root  operator  512 Aug 22 00:51 .snap
-rw-r--r--  1 root  wheel      17 Aug 22 00:51 poc
root@hg:/usr/home/nf # cat /mnt/poc
proof of conecpt

As can be seen above, the kernel recognised the legacy geom mirrored disks and performed a metadata upgrade from v3 to v4. To further this I prove that the original data can be read back.

So if anyone is thinking of moving GEOM based disks from an old BSD box to a newer distribution, fear not - as usual BSD is rock steady and can be relied upon!