Gconcat on FreeBSD

The last time I wanted to combine two smaller drives into a single virtual drive on FreeBSD I used Gvinum. Ceri Davies posted a helpful comment indicating I should try using gconcat(8). I did that today and thanks to an insightful piece of advice from Robert Watson, I got it working.

This is what the drive looked like.

shuttle01# df -h
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ad5s1a    496M     36M    420M     8%    /
devfs          1.0K    1.0K      0B   100%    /dev
/dev/ad5s1f    989M     22K    910M     0%    /home
/dev/ad5s1h     54G    4.0K     50G     0%    /nsm1
/dev/ad7s1d    361G    4.0K    332G     0%    /nsm2
/dev/ad5s1g    989M     12K    910M     0%    /tmp
/dev/ad5s1d    1.9G    531M    1.3G    29%    /usr
/dev/ad5s1e    4.8G    1.6M    4.5G     0%    /var

I want to create /dev/concat/nsm. However, if I try to do that while /nsm1 and /nsm2 are mounted I'll get errors like this:

shuttle01# gconcat label -v nsm ad5s1h ad7s1d
Can't store metadata on ad5s1h: Operation not permitted.

So, unmount /nsm1 and /nsm2 before continuing. Next:

shuttle01# umount /nsm1
shuttle01# umount /nsm2
shuttle01# gconcat label -v nsm ad5s1h ad7s1d
Metadata value stored on ad5s1h.
Metadata value stored on ad7s1d.
Done.
shuttle01# ls /dev/concat/nsm
/dev/concat/nsm
shuttle01# newfs /dev/concat/nsm
/dev/concat/nsm: 438631.6MB (898317520 sectors) block size 16384, fragment size 2048
        using 2387 cylinder groups of 183.77MB, 11761 blks, 23552 inodes.
super-block backups (for fsck -b #) at:
 160, 376512, 752864, 1129216, 1505568, 1881920, 2258272, 2634624, 3010976,
...truncated...

Now I can create /nsm and mount it.

shuttle01# mkdir /nsm
shuttle01# mount /dev/concat/nsm /nsm
shuttle01# df -h
Filesystem         Size    Used   Avail Capacity  Mounted on
/dev/ad5s1a        496M     36M    420M     8%    /
devfs              1.0K    1.0K      0B   100%    /dev
/dev/ad5s1f        989M     22K    910M     0%    /home
/dev/ad5s1g        989M     12K    910M     0%    /tmp
/dev/ad5s1d        1.9G    531M    1.3G    29%    /usr
/dev/ad5s1e        4.8G    1.6M    4.5G     0%    /var
/dev/concat/nsm    415G    4.0K    382G     0%    /nsm
shuttle01# touch /nsm/test

Cool. If I don't want to use it again:

shuttle01# umount /nsm
shuttle01# gconcat stop nsm
shuttle01# gconcat unload
shuttle01# ls /dev/concat

To use it again:

shuttle01# gconcat load nsm
shuttle01# ls /dev/concat/nsm
/dev/concat/nsm
shuttle01# mount /dev/concat/nsm /nsm
shuttle01# ls /nsm
.snap   test

Remember to enable gconcat in /boot/loader.conf:

shuttle01# cat /boot/loader.conf 
geom_concat_load="YES"

Remember to edit /etc/fstab. The original looked like this:

# Device                Mountpoint      FStype  Options         Dump    Pass#
/dev/ad5s1b             none            swap    sw              0       0
/dev/ad5s1a             /               ufs     rw              1       1
/dev/ad5s1f             /home           ufs     rw              2       2
/dev/ad5s1h             /nsm1           ufs     rw              2       2
/dev/ad7s1d             /nsm2           ufs     rw              2       2
/dev/ad5s1g             /tmp            ufs     rw              2       2
/dev/ad5s1d             /usr            ufs     rw              2       2
/dev/ad5s1e             /var            ufs     rw              2       2
/dev/acd0               /cdrom          cd9660  ro,noauto       0       0

The new one looks like this:

# Device                Mountpoint      FStype  Options         Dump    Pass#
/dev/ad5s1b             none            swap    sw              0       0
/dev/ad5s1a             /               ufs     rw              1       1
/dev/ad5s1f             /home           ufs     rw              2       2
#/dev/ad5s1h            /nsm1           ufs     rw              2       2
#/dev/ad7s1d            /nsm2           ufs     rw              2       2
/dev/ad5s1g             /tmp            ufs     rw              2       2
/dev/ad5s1d             /usr            ufs     rw              2       2
/dev/ad5s1e             /var            ufs     rw              2       2
/dev/concat/nsm         /nsm            ufs     rw              2       2
/dev/acd0               /cdrom          cd9660  ro,noauto       0       0

I'm deploying this system in a RAID 0 configuration because it's a Shuttle with two HDDs. I'm not worrying about recovering from a disaster with this box. It's going to help with the ShmooCon network. If I had three or more drives I'd consider using gstripe(8).