How to: Expand your Synology RAID volume

The website has been down for maintenance recently while i replace the HDD’s and expand my RAID volume in my NAS server. It seems 4TB just isn’t enough for my ever expanding film collection, you can thank High Definition and Blu-Ray discs for that.  Anyway, i decided to purchase 4 x 3TB Western Digital RED NAS Edition (WD30EFRX) HDD’s to replace my ageing but still very reliable 1TB Samsung Spinpoint F1 HDD’s. This would give me a sizeable increase in storage capacity and hopefully mean i won’t have to upgrade again for some time.

My intention was to replace 1 HDD at a time and then expand the RAID volume as suggested in the Synology FAQ. Unfortunately this wasn’t possible as the original RAID  volume was created by the binary “mdadm 0.9 version”. The new one is the mdadm 1.2 but a 0.9 mdadm volume can’t be converted directly to a 1.2 volume. This was completely unexpected and stopped me in my tracks.

The error message i got when selecting ‘Repair Volume’ is shown below:

“The volume is created with a previous version of DSM which does not support hard disks larger than 2TB. To use hard disks larger than 2TB, please create a new volume with the latest version of DSM”

I consulted Synology Technical Support (Who were fantastic coincidently, very knowledgeable, helpful and prompt to respond) and they suggested the following resolution:

  1. Upgrade DS to DSM4.1 (I already had the latest version)
  2. Create a new Volume2 with the 3TB disk (this one will be new volume type which supports 3TB disks fully) and create a folder backup on it. Using the function “Local Backup” to backup the data from Volume1 to Volume2. (Luckily there was sufficient space to do so with the new 3TB disk)
  3. Delete the Volume1 and recreate a new one Volume1 with three 3TB disks. This time the Volume1 will be new type, Synology Hybrid RAID or ‘SHR’. Then restore the data from Volume2 to Volume1 by the function local backup.
  4. After restoring the data from the Volume2 to Volume1,  delete the Volume2 to release the 3TB disk.
  5. Join the 3TB disk to Volume1 and expand the Volume. There is a tutorial here on how to expand a volume.

I followed these steps to the letter and now i have a new volume 1 which consists of 4x 3TB Western Digital RED NAS Edition HDD’s. Importantly i haven’t lost any data and all my settings have been restored which saved me a lot of manual tinkering. While this process has been fully successful it hasn’t been without incident. Firstly i was expecting to be able to expand the original volume which wasn’t possible, and there was no indication on any forum or website that this wouldn’t be possible. Secondly the whole upgrade process has taken considerable time to complete, rebuilding a 3TB raid array is not a quick process, and copying data back and forth from different volumes and external disks (golden rule – always take a backup) also took a long time.



8 thoughts on “How to: Expand your Synology RAID volume

  1. Hi Pete, thank you for this great article. Im facing a same problem with my DS411+II. I just waited too long and now my 4x2TB disks are full, so with one 4TB disk I dont have enough space to do a Volume1 backup. Anyhow I will manage to backup the data partially on an externat 2TB USB drive and the rest should fit on 4TB Volume2. Now I have a question, when you removed your 3x1TB (old drives) and delete Volume1 where from did the DiskStation booted from? From the newly created Volume2? You also had all 4x1TB fitted in your NAS I suppose. You remove one of four so the Volume1 is signaled as crashed but functional. You then created Volume2 on new 3TB disk and power the NAS off after backup. Then remove the remaining three 1TB drives and replace them with new 3x3TB. When you power on the DiskStation the system (DSM) could boot only from Volume2. Can you confirm so that I can move on with my upgrade. Thank you again.


    • Hi Erik,

      Once you have removed the 3x old drives, and inserted the 3x new drives you will create a new SHR volume1 on those three new drives. You then perform the local backup function again to copy across all the data. This is Step 3 of the process above.

      The system boot partition will be recreated in the process. Think of it as a Rubiks cube, your moving one side to make way for another, once that is in place your moving it back to it’s original position.


  2. Hi Pete,

    Similar sort of question. I have a DS209. Do I need to delete volume 1 with the old original disk or do I just replace it with the new HDD and it will just create a new volume 1 without having to delete anything?


  3. Hi mcat, once you have replaced the first disk and copied the data over to the new Volume2, replace the 2nd disk (you don’t need to delete Volume1, you can just replace the disk) and then create a new Volume1. Then copy the data back to the new Volume1, delete Volume2 and then expand Volume1 to cover both disks.


  4. Hi Pete!
    I wish to thank you very much for your post! It was really helpful to me, I followed the entire process and upgraded my 2x2TB hd in a DS209 to 2x4TB flawlessly! Synology support wasn’t neither fast nor helpful to me.


  5. Hi, am I so late?? .^^.
    I have a question. I have One Disk 1TB. So I want to change old 1TB to new 3TB.
    How to migration to new3 TB?
    As your explain, I guess following in my case.

    1. Old Disk 1TB (Fully Data) Vol1
    2. Backup Disk 1TB over. Vol2
    3. New 3TB Disk.

    At backup and restore menu, backup Old 1TB(vol1) to Vol2.
    and remove vol1(old 1TB).
    And create vol1 with New 3TB.
    And Restore From Vol2 to Vol1(New 3TB).

    Am i right??

    So, I need two disk, backup disk(1tb over) and 3TB for New VOL1.

    Is there anyway how to directly migrate 1TB to New 3TB?


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