Change disks in DS220j with higher capacity

Is there a simple tutorial available for replacing 2x 1Tb disks in a Raid configuration in DS220j with disks of higher capacity (2x 4Tb)?
DSM 7.2

DISCLAIMER: I don’t have a Synology, so someone should correct me, if there are any errors.

There is a how-to page by Synology… maybe this already helps. It seems to be relatively straight-forward:

But how to proceed depends on what kind of RAID you are currently using.

If you have a RAID0 or JBOD (“Basic”), your data is striped or distributed across both drives, so you can’t just exchange a drive. You’ll first need to backup all your data to an external USB drive (or a second Synology), then replace the drives, choose a RAID version and format them, and then copy back the data.

Nota bene: As Synology rightfully says, it’s prudent to backup your data, even if you’re using RAID1 (mirror) or SHR (Synology Hybrid RAID). But you will definitely still have a copy of your data on the 1TB HDDs, in case something goes wrong.

If you are using SHR or RAID1, you should be able to upgrade easily. With SHR and RAID1 plus a Synology model with only two HDD slots and no free slots, you have to replace one drive at a time, so the RAID can rebuild itself before the second drive is replaced. This is the tutorial at the very end of the Synology page. It is for an SHR setup, but should be the same for a RAID1.

After the RAID has been rebuilt a second time for the second 4TB HDD, you should also check the size of your volume in DSM’s Storage Manager. Afaik, newer versions of DSM will auto-increase the volume size, but if not, you have to do it manually.

Think on reflection that I might just buy a new DS223j and repurpose the old DS220j (or flog it off).

So, to conclude this topic I have managed to perform this task successfully, increasing the Storage Pool capacity from 1TB SHR RAID to 4TB using 2 x Synology 4TB HAT3300 HDDs using the instructions in this YT resource.
As the video is from 2020, it’s a little out of date as probably features DSM version 6 (mine is DSM 7.2) but it is still easy to follow if you follow the instructions on the screen as it progresses. The screen instructions are intuitive and worthy of the Synology brand.
This video gave me the confidence to tackle this task and it worked really well. It mentions consecutive 24 hour periods for the disk to repair but under DSM 7 the option for fast repair is now available and in my case it took about 1½ hours for the first replacement disk and 50 minutes for the second (the 1TB pool was ~60% to capacity).
I chose the Synology brand NAS’s in preference to the Seagate IronWolf because the Synology disks firmware can be updated automatically by the Package Manager behind the scenes.

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