Multiple Vertical Expansions --> Performance Drop? --> 'Refresh' X-RAID2 without Factory Default?

Hi All,

My TL;DR question is: -

Would multiple X-RAID2 expansions cause a degradation in SMB write performance and if so, is there a way of recreating the X-RAID2 array and Volume/Shares from scratch and restoring data from backup to regain performance without performing a factory default reset?

The context for the question is: -

I have a Primary NAS RN214 running OS 6.10.9 and a Backup NAS RN104 running OS 6.10.10.

Both have 2x3TB + 2x6TB drives after a vertical expansion carried out via advice in this forum in 2021. Both NAS were expanded without any issues through the UI (one disk at a time) and without any need to factory default + restore data. They are both using X-RAID2 (RAID 5) with a single Volume and multiple identical shares.

On reaching the data limit of my Primary NAS, I decided to buy 2x8TB drives and perform another vertical expansion. At the same time, I decided to 'swap' the 2x6TB drives from the Backup to the Primary and vice versa as the Backup NAS runs only weekly backups and the drives have led a less stressful life. 

Doing this 1 disk at a time has taken a few days(!), but I am back up and running with fully redundant volumes.

However, I have noticed what appears to be a marked reduction in write performance to the Primary NAS. Over a gigabit network, I rarely get anything above 40MB/s (using SMB from multiple wired Windows 11 PC's), when I would routinely see 80-100MB/s.

I believe that the various expansions over time may have caused this, but I'm not sure. I understand that the expansion process might add RAID layers which are invisible to me through the admin UI, but which might cause overhead.

If the X-RAID2 array does need to be refreshed - I would like to understand if this is possible without performing a factory default and having to reinstall Plex and setup all my backup jobs, users, config etc etc.

Many Thanks!