Advice to migrate from a dead DS1821+ with 4-drive SHR storage pool (and died while expanding) to a DS1525+

Synology
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I’m looking for advice on exact steps to take in my situation once I get my replacement NAS.

I was expanding my one SHR storage pool in a DS1821+ that had 4 Drives, by adding just one drive. Something happened across the UPS IEC cable connected to the NAS where it crackled, and suddenly the NAS died. It won’t power on at all, no lights or sound.

I’m hoping the drives survived. The 4 installed ones passed their Extended Smart Test and went through a data scrub a few days ago. The new one passed its SMART and Surface Read/Write Test. The DS1821+ was updated on the latest DSM available just recently before starting the expansion.

It seems “HDD Migration” is the only option here. But I’m not sure of the exact steps or precautions when dealing with a new NAS.

  1. Would I be placing the drives into the new NAS before turning it on for the first time?
  2. Before the old NAS died in the middle of expansion, would be adding just the original 4 drives first? And later add that 5th one that was interrupted in the expansion? Or would I place them all from the start?
  3. I’m worried about dealing with SSD cache. SpaceRex’s video mentioned it’s best to disable it before the HDD Migration, and to re-enable once in the new NAS. This sentence from this Synology page worries me:
    “If your source NAS is broken and you force migrate when you are advised to remove SSD cache first, the data in the volumes will not be accessible after migration.” Is disabling it something you can do within the new NAS before migration, or it had to be done in the old one? If so, how do you deal with this when the old one is dead? I haven’t found a video going over setting up a completely new untouched NAS for migration yet.

Any advice appreciated :folded_hands: I’m mainly concerned about data instead of NAS settings.

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A few things worth knowing before you start. The slot order matters in HDD migration — note which drive is in which bay before you pull them. If you cannot check the original NAS directly you can usually figure it out from the SMART data labels if you marked them when you installed them. The bigger complication here is that the expansion was mid-flight when the NAS died. The pool is in an unknown state — it may have written partial SHR metadata for the 5th drive. Because of this I would recommend installing only the original 4 drives first, then powering on the DS1525+. Let DSM assess the pool and get it to a healthy state before you touch the 5th drive. If the expansion had not yet committed, DSM will just see a 4-drive SHR pool in good shape. If it was partially committed you may see a degraded pool — do not panic, let parity sync run completely before adding anything else. Once the 4-drive pool is confirmed healthy in Storage Manager, then add the 5th drive and resume the expansion properly on the new NAS. One note on the DS1525+: it has 5 bays versus the DS1821+'s 8, so your future expansion headroom is limited. Worth knowing if you planned to grow the array further down the line.

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This is completely untrue. This is software RAID. DSM stores the drive info, Drive order is immaterial. You can swap drive slots as often as desired (with NAS powered off).

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