FreeNAS Resize Root Partition

FreeNAS designed to fix into sdcard, the default root partition only come with 1GB, it's insufficient if you try install mediatomb + transcoder. Below is steps on how to resize the root partition of FreeNAS.
Before proceed, boot into option 4 (single user mode) for all steps below.

1. )  Add another disk to NAS machine or virtual disk if running on VM.

2. )  Backup the current partitions for reference, type:
# gpart backup da0
<da0> is the geom label, your case may difference.

3. ) Backup all partition to new added disk.
# dd if=/dev/da0s1 of=<new disk path>/da0s1
# dd if=/dev/da0s2 of=<new disk path>/da0s2
# dd if=/dev/da0s3 of=<new disk path>/da0s3
# dd if=/dev/da0s4 of=<new disk path>/da0s4

4. ) Delete and re-create the partition so that we have the free space for 1st partition.

# gpart show da0
=>      63  18874305  da0  MBR  (9.0G)
        63  1930257    1  freebsd  [active]  (942M)
  1930320   1930257    2  freebsd  (942M)
  3860577      3024    3  freebsd  (1.5M)
  3863601     41328    4  freebsd  (20M)
  3904929       14969376       - free -  (7.1G)

# gpart delete -i 4 da0

you need calculate the start index of your last partition, your last partition index should be 18874305 - 128 - 41328.

# gpart add -t freebsd -b 18832849 -s 41328 da0

5. ) Repeat step 4. for partition 3 and 2. You should get something like below
# gpart show da0
=>      63  18874305  da0  MBR  (9.0G)
        63  1930320    1  freebsd  [active]  (942M)
  1930383       14969241       - free -  (7.1G)
  16899624   1930257    2  freebsd  (942M)
  18829881      3024    3  freebsd  (1.5M)
  18832905     41328    4  freebsd  (20M)

6. ) Restore the partition 2,3 and 4.

# dd of=/dev/da0s2 if=<new disk path>/da0s2
# dd of=/dev/da0s3 if=<new disk path>/da0s3
# dd of=/dev/da0s4 if=<new disk path>/da0s4

7. )  Resize root partition
# gpart resize -i 1 da0

8. ) Correct the label
# bsdlabel /dev/da0s1
# /dev/da0s1:
8 partitions:
#          size     offset    fstype   [fsize bsize bps/cpg]
  a:   1930241         16    unused        0     0  
  c:   1930257          0    unused        0     0     # "raw" part, don't edit

Edit the label to correct size.

#  gpart show da0

=>      63  18874305  da0  MBR  (9.0G)

        63  16899561    1  freebsd  [active]  (8.1G)

  16899624   1930257    2  freebsd  (942M)

  18829881      3024    3  freebsd  (1.5M)

  18832905     41328    4  freebsd  (20M)

  18874233       135       - free -  (67k)

 Mine da0s1 size is 16899561, I edit my label as below:

# /dev/da0s1:

8 partitions:

#          size     offset    fstype   [fsize bsize bps/cpg]

  a:   16899545         16    unused        0     0   

  c:   16899561          0    unused        0     0     # "raw" part, don't edit

9. ) Now grow the file system

# growfs /dev/da0s1a

10. ) Reboot the machine and you will find that the root / not able to mount

type ufs:/dev/da0s1a to mount root.

11. ) Correct the mount path for root /

# mount -uw /

# vi /conf//base/etc/fstab

change /dev/ufs/FreeNASs1a / ufs ro 1 1

to /dev/da0s1a / ufs ro 1 1

12.) Reboot and done.