I have a 10x4TB SnapRAID config with the 8 x data drives in a single unionFS coming off an IBM ServeRAID M1015 controller in "IT Mode" and 2 x drives connected via USB 3.1 as parity. This has been working well for me for sometime and transfer rates have always managed to saturate my 1Gbps network.
Last week I started having issues with file systems being intermittently unavailable which was followed by all my devices attached via my M1015 dropping out. Seemed a little suspect to me so I shut down my NAS fully for around an hour and then booted it back up. Everything seems to be functioning, however I have noticed now that transfer speeds are massively decreased (locked at 3.5MiB/s) and it doesn't seem to matter what protocol I am using (have tried SMB, FTP and SFTP).
My M1015 is several years old now and am wondering if it is on the way out. Are there any tools I can use to probe/test hardware or specific log entries I should be looking at that might give me some insight. Good news is these controllers are still plentiful and cheap, bad news is I have completely forgotten how I managed to flash the firmware. Anyway, first things first I guess.