Migrating from a Synology 8 bay NAS to a 6 bay NAS

I currently have a Diskstation 1813+ 8 bay NAS which is doing a great job, but since Synology gave me a 1618+ to review, and the 1813+ is 7 years old, I’m migrating over to that instead. The catch is that I have 7 drives already in the 1813+ in a single SHR setup. How do I get that across to the newer 6 bay NAS? This is actually a writeup of the planned migration, rather than the success at the end… and the goal is to reduce costs. I could just buy 6 new 10TB drives and have an easy migration!

Yes, I’ve lied in bed at night thinking about this and the best approach. I have 40TB of space, ~30TB in use in a SHR setup:

If I had somewhere to just copy 30TB of data to temporarily, it’d be easy. Copy the data off, move 6 of the drives, create a new SHR, copy the data back and done. Except, I don’t have 30TB of space anywhere.

It isn’t possible to take a disk out of the SHR setup (i.e. shrining the volume size and somehow telling it to abandon one of the disks), so I can’t get a disk that way. I can however, take one disk out and break it’s redundancy while moving data. Risky, but that could give me at least the 12TB disk to use as temporary space. That’s a start.

It’s unavoidable, I’ll need to buy some more disks for temp space. I can get two external 10TB Seagate HDD for $283AU each and use those as temporary space along with the 12TB disk. That’ll get me my 30TB to copy everything off while I juggle the rest of the disks.

That leaves me with 2x 10TB and 4x6TB in the old SHR setup. There is a limitation of SHR which is worth understanding:

For SHR: The capacity of the drive you intend to add must be equal to or larger than the largest drive in the storage pool, or equal to any of the drives in the storage pool.
Example: If an SHR storage pool is composed of three drives (2 TB, 1.5 TB, and 1 TB), we recommend that the newly-added drive should be at least 2 TB for a better capacity usage. You can consider adding 1.5 TB and 1 TB drives, but please note that some capacity of the 2 TB drive will remain unused.

https://www.synology.com/en-au/knowledgebase/DSM/help/DSM/StorageManager/storage_pool_expand_add_disk

What that means is, if I take the very slow approach of building up a SHR with just the two 10TB disks, then look to add more disks after, I can’t add a 6TB disk.

However, I can move all 6 remaining disks across and create a new SHR giving me a bit over 30TB:

Once that’s done, I can then copy all the data off the temporary 2x10TB and 1x12TB disks to the new Synology DiskStation 1618+. Great, except I want to use all four 6TB disks elsewhere and the end result would leave me with 4x10TB, 1x12TB and 1x6TB. I can’t remove the last 6TB disk without having an equal or bigger disk to replace it with, and I don’t want to but a third 10TB disk at this stage.

What I can do is set up the SHR being 1 disk short, leave out the last 6TB disk so I have 2x10TB and 3x6TB, which will give 28TB of space. Enough that I can then copy the contents of any two of the three temporary stoage disks (2x10TB and 1x12TB), and as they get cleared, add them to the SHR.

Each time I add a disk to the SHR it might take a day or two though – this process will take a while. I’ve got multiple points of failure (original SHR has no redundancy, single temporary storage disks all have no redundancy). I can only change one disk at a time.

Once I’m at 4x10TB and 1x6TB in the new SHR, I’ll have enough room to copy the 12TB of data off the spare disk, onto the SHR, then swap out the 6TB for the 12TB.

I also need to make sure for my own neatness, that the 6th bay doens’t have a drive in it at any time. Drives can’t be physically moved around in a SHR, so I don’t want to have 5 drives in a 6 bay NAS and have a ‘gap’ in the middle where there isn’t a drive. Not a dealbreaker on the move, but still :)

In summary:

  • Buy 2x10TB drives
  • Copy 20TB of the 30TB to the two drives I bought
  • Remove 1x12TB drive from SHR in the 1813+ NAS and break redundancy.
  • Copy remaining data to the 12TB drive mounted somewhere else.
  • Move 2x10TB and 3x6TB into the new 1618+NAS and create a SHR.
  • Copy the data off the 2x10TB drives to the new SHR.
  • Swap out one 6TB drive for a 10TB drive and repair the array.
  • Swap out the other 10TB drive for another 6TB drive in the array.
  • Copy the data on the 12TB disk onto the SHR.
  • Swap in the 12TB drive with the final 6TB drive.
  • All 6TB drives can go back in the 1813+ for other purposes

I think that’s my plan. I’ll update this post once I’m at the end of it (currently awaiting the arrival of the 2x10TB drives). Can you poke any holes in my plan?

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