This article describes the process to increase the disk capacity of a ReadyNAS Duo configuration from 1 TB to 2 TB In my case, my X-RAID configuration was broken due to a faulty disk. I took the opportunity to repair the redundancy and also to increase the capacity. The process is simple but very long. It took me 4 days, several reboots and many disk synchronisation.

To replace the 1TB disks, I bought two Seagate ST2000DL003-9VT166 hard disks which offer 2TB (they are referenced in the hardware compatibility list). I then followed the following process :

1. Upgrade to the latest RAIDiator firmware (4.1.7)
2. Replace a first disk by the new larger disk (in my case the faulty disk)
3. Wait until the disks are fully synchronized (Status should be Redundant)
4. Shutdown properly and restart the ReadyNAS
5. Make sure the disks are fully synchronized. If not, wait for synchronization to finish.
6. Replace the second disk by the larger disk
7. Wait until the disks are fully synchronized (Status should be Redundant)
8. Shutdown properly and restart the ReadyNAS
9. After the reboot, the ReadyNAS triggers a disk expand
10. Another reboot is necessary after which ReadyNAS triggers the file system expansion

ReadyNAS Disk Expansion

The disk expansion happens at the very end and is fairly quick. Before the disk expansion, and when the new disks are installed, you will see that the disk partition table has not changed. The fdisk /dev/hdc command reports:

Device Boot   Start      End      Blocks   Id  System
/dev/hdc1         1      255     2048000   83  Linux
/dev/hdc2       255      287      256000   82  Linux swap
/dev/hdc3       287   121575   974242116    5  Extended
/dev/hdc5       287   121575   974242115+  8e  Linux LVM

Since ReadyNAS uses LVM to manage the disks, you can use pvdisplay to look at the available space. At this stage, everything is used.

nas-D2-24-F2:/var/log/frontview# pvdisplay
  --- Physical volume ---
  PV Name           /dev/hdc5
  VG Name           c
  PV Size           929.09 GB / not usable 0   
  Allocatable       yes (but full)
  PE Size (KByte)   32768
  Total PE          29731
  Free PE           0
  Allocated PE      29731
  PV UUID           huL1xb-0v0O-vJ6K-LqaK-P4kf-q4Wm-SFeYCX

After the reboot, the ReadyNAS will start the disk expand process. It will do this only if the two disks are redundant. After expand, the partition looks as follows:

Device Boot    Start       End      Blocks   Id  System
/dev/hdc1        1       255     2048000   83  Linux
/dev/hdc2      255       287      256000   82  Linux swap
/dev/hdc3      287    243201  1951200343    5  Extended
/dev/hdc5      287    121575   974242115+  8e  Linux LVM
/dev/hdc6   121575    243200   976950032   8e  Linux LVM

Once the partition table is fixed, you are asked to reboot:

The first stage of the in-place volume expansion is done.
Please reboot the device to complete the volume expansion.

After the reboot, the LVM volumes are increased. You can check with pvdisplay which now reports the new disk partition and with lvdisplay which takes into account the two physical volumes.

nas-D2-24-F2:~# pvdisplay
  --- Physical volume ---
  PV Name               /dev/hdc5
  VG Name               c
  PV Size               929.09 GB / not usable 0   
  Allocatable           yes (but full)
  PE Size (KByte)       32768
  Total PE              29731
  Free PE               0
  Allocated PE          29731
  PV UUID               huL1xb-0v0O-vJ6K-LqaK-P4kf-q4Wm-SFeYCX
   
  --- Physical volume ---
  PV Name               /dev/hdc6
  VG Name               c
  PV Size               931.69 GB / not usable 0   
  Allocatable           yes (but full)
  PE Size (KByte)       32768
  Total PE              29814
  Free PE               0
  Allocated PE          29814
  PV UUID               TOqmR2-fYOq-jf0q-n1ka-N9K1-B2CB-oyU23Y

nas-D2-24-F2:~# lvdisplay
  --- Logical volume ---
  LV Name                /dev/c/c
  VG Name                c
  LV UUID                2CzUXf-uzSD-DGcS-KePF-6elz-XveS-xePwHf
  LV Write Access        read/write
  LV Status              available
  # open                 2
  LV Size                1.82 TB
  Current LE             59545
  Segments               2
  Allocation             inherit
  Read ahead sectors     0
  Block device           254:0

The last step is now to resize the file system. The ReadyNAS reports the following alter the LVM volume is expanded:

Your system will now begin online expansion. 
Please do not reboot until you receive notification that the expansion is complete.

And while the expansion is in progress, you will see that the ReadyNAS uses resize2fs to grow the file system. If you look at the running processes, you will see the following:

root 1371  ?  S    21:41   0:00 /bin/bash /frontview/bin/expand_online
root 1537  ?  Ss   21:41   0:00 /frontview/bin/blink_expand
root 1538  ?  S    21:41   0:42 resize2fs -pf /dev/c/c

Data volume has been successfully expanded to 1853 GB.

nas-D2-24-F2:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/hdc1             1.9G  590M  1.3G  30% /
tmpfs                  16k     0   16k   0% /USB
/dev/c/c              1.8T  888G  966G  48% /c

Problems and hints

• If at some point, the ReadyNAS enter in re-synchronization after a reboot even if disks are already synchronized. Check that the disks are in good health. Look at the /etc/rc3.d directory and make sure the rc3 script is called only once through the Sxxx symbolic links (See Frontview shows 100% disk usage)
• If you suspect something wrong, use ssh to connect to the ReadyNAS and look at /var/log/messages or /var/log/kern.log to see if there is not some hardware issue.
• Check the file /etc/frontview/raid.conf and verify that the two lines are similar and indicate the reference of your new disk (this file is rebuilt after each reboot).
• Look at the /proc/xraid/configuration file. It indicates a lot of information about the current X-RAID status and synchronisation process.
• At the last resort, read and understand the /etc/hotplug/sata.agent script which contains the details of the resynchronisation and expansion process.