Running vanilla Debian.
Got a mdad raid 5 with 4 disks. All the disks are the same.
Running in a sabrent 5 bay, one bay is empty.
Moved the 4-disk raid into a 4 bay sabrent to test and visa versa.
Consistently, when I cannect this raid to any machine, it constantly accesses the raid at about 2mb/s.
Its only been Debian I've connected to, but both plasma and gnome. This particular set of disks will just do that.
Snooped around for processes doing it, and finally found a that the accessor is always associated with plasma or gnome desktop processes.
Mdadm shows no anomalies. Or tasks, or processes running.
Finally took the step of nuking the raid and rebuilding from scratch cause I thought made it was built properly to begin with and there was a sneaky scrub going on in the back. Nope. Does it again.
Any suggestions? Bad disk, or a disk going bad? I've isolated as much as I can here I think.