Performance halved at a stroke (ReadyNAS Duo, 4.1.8) ...

In a busy few weeks, my little ReadyNAS Duo's performance seems to have halved at a stroke. The problem seems to be a consequence of upgrading to RAIDiator 4.1.8 (release) and performing a full factory reset but ... just in case ... here's a full rundown of its recent life ...

* After swapping my ageing PC for a shiny new iMac (really shiny, by the way), I noticed a very modest (but welcome) *increase* in performance from the ReadyNAS.
* Running Windows 7 (directly through Boot Camp, fully Windows Update'd) and RAIDiator 4.1.8 beta (for Lion compatibility) the little Duo could saturate my Gigabit Ethernet to 25-30% (transferring data at around 250-300Mb/s, then). Everything was running great ...
* Then a mini-disaster ... after three years use the ReadyNAS power supply gave up. The unit shut down without warning and wouldn't power up again.
* Some excellent online support put me back on track. "Some time later" and with a new power supply connected (an identical Netgear part) I was up and running again.
* The unit started first time and all was well ... everything was accessible and usable ... but restarting the unit once more (from front-view) the ReadyNAS unexpectedly froze on boot.
* Blue light flashing at 1Hz, fan at medium-volume, no activity or drive lights and invisible to RAIDar, I gave it four/five hours ...
* Not responding to physical (power) button presses, I had to pull the plug. Fortunately, the unit picked itself up and booted without issue. Scouring downloaded log's I could see *no trace whatsoever* of the failed boot.
* To eliminate any possibility of data corruption or similar badness (and with a new release-version of RAIDiator 4.1.8 now available) I updated the unit firmware, performed full factory reset and reconfigured the unit to match its old settings (all from front-view). Perhaps this was a beta glitch?
* Now running solidly and without issue, I copied data back to the unit using Windows Explorer and a local backup. It should have close to zero fragmentation, then.

Doing this, it was clear performance had halved. The unit now saturates just 10-15% of the network ... transferring at around 100-150Mb/s only (no RAIDar or front-view pages open).

This doesn't look like a hardware problem ... the drives look fine (a matched Seagate ST3500630AS pair, their SMART reports look good and their temps are normal), the network looks fine (private LAN, both Mac (on-board Broadcom NetXtreme) and NAS are wired to the same Netgear WNDR3700 (gigabit router, latest firmware), no concerning errors ... a few TCP retransmits which are not unusual) and there are no errors or warnings in the logs. But for a new power adapter, nothing has changed hardware-wise.

The old and new front-view settings match near-exactly (same network settings, same shares, same users and access rights, one or two *fewer* services running than before, no bittorrent/photo's/remote/vault, full data journaling, oplocks enabled, fast CIFS writes enabled, jumbo frames disabled), the unit isn't resynching or indexing media, there are no scheduled backup jobs (internal or time machine) and ... to be absolutely sure ... I've also confirmed performance several times over the last week to eliminate any other invisible, transient activity ... no luck :?

Performance seems to have halved at a stroke with no clear reason.

It looks very much like a RAIDiator 4.1.8 issue but I'm happy to help troubleshoot. Any chance a Jedi (or other expert) can help?

Thanks,

Justin