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I have a small Synology NAS with 2-bay and 4TB HDD on each bay. It’s configured in RAID 0 (Yes, I know. I like to live dangerously).

I would like to upgrade both drives to 8TB but for that to happen, I would have to copy the data from the NAS to another place, install the new disks and copy it back.

Well, I don’t have a third 8TB available to do that. I also don’t think I could just remove the two 4TB drives and remount some place else without losing the data like I would do with a regular external drive.

I was thinking about using a cloud service but I wasn’t able to find any service that will accept 8TB of data without file size limit and keep it there when the sync is gone.

Any advice or ideas on how can I extract the data to copy it back to the new drives?

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    If I were doing this I would get an 8 TB external USB drive and back up to that
    – John
    Dec 21, 2019 at 17:57
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    There is no generic way to deal with cases like this because RAID implementations tend to differ from device to device. I mean, maybe in the case of a Synology device things might be more standardized, but still… This is 8TB of data on two 4TB hard drives. The best and simplest solution is to get an external 8TB hard drive, transfer the Synology data to that 8TB hard drive, upgrade the drives in the Synology and copy the data back. Dec 21, 2019 at 18:14
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    Introducing… the Tower of Hanoi ;) You must have another location as an intermediate.
    – Tetsujin
    Dec 21, 2019 at 19:28

1 Answer 1

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You have 2 bays. You **need* both 4TB disk in it to access their data. So that is it. End game. There is no generic way to pull one disk, still have access to your data, and put in a new target disk.

You would either need:

  • The ability to use a third disk in the NAS
  • Or use external storage as intermediate.

You also want to have a backup in case things go wrong. Which could be simple user error, or power failing at just the wrong time.



Thus the only logical solution would be:

  1. Mount a 8TB disk elsewhere (put it in a PC, on an USB enclosure on the pc, USB enclosure on laptop, USB on a router (many seem to have that these days), ... anywhere. and copy all data to it.
  2. Pull both 4TB drives

Now it gets interesting. If you want to go back to RAID0/stripe that you need both 8TB drives. So


  1. Mount both 4TB drives in a PC, format them. (Any way. JBOD, stripe, ... as long as you get 8TB storage space).
  2. Copy the data from the 8TB drive to this
  3. Insert both 8TB drives in the NAS, initialise, copy the data from the PC.


If you wanted to change from stripe to mirror, it gets easier.

  1. Put in the empty 8TB disk
  2. Create a RAID mirror with one disk missing (not sure how to do that on a NAS from command line, but mdadm has the --missing parameter).
  3. Copy data to broken RAID
  4. 'Replace' missing disk. Fix RAID.

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