Just in the last few months, I've noticed a HUGE decrease in access speed in our office TS3400. It's setup as a RAID5 (as it has since day 1). I thought possibly it could be a bug so when the latest firmware came out not too long ago, I tried that and it seemed to make no difference. I've done a RAID scan and everything comes back as ok. I even went as far as disconnecting it from the network, and connecting it directly to a laptop to test for the latency and I get the same issue...slow network access (saving or reading) - just pulling up a directory structure there's sometimes a long pause. While there are a great number of files on there (probably a couple hundred thousand between all the shares), they're only occupying a little over 1TB of space. A solid example - I transfer a 4GB ISO file - while directly connected or connected thru the network, I still get only (on average) 17Mbps throughput on a 1Gbps connection. And again, this NEVER used to happen - it used to be pretty quick...
Just some background - this unit is about 2-3 years old, but never had issues with it.