Hi guys, thanks so much for your input, your experience is really appreciated.
@mikeiver1: Good thought, so I cracked the lid and have been running lid-free (after a couple of reboots and cool-down for an hour or so). The clicking is obviously noisier (!) but alas is still present.
@ALucas: The heads only seem to go crazy for a few minutes at boot-up as soon as the NASlite+ OS is loaded and operational. I'm assuming this is something to do with a SMART scan (even though I have this disabled), but is this unusual? Otherwise, the annoying clicking just sounds like the heads parking and then being slightly disturbed so they need park again, every 9 seconds. Certainly doesn't sound dangerous (fingers crossed) but it is annoying since I've never heard drives behave like this and I'm trying to make a quiet system.
@Grumpa: Good idea, and after looking I found the unit only has a 152W PSU. This should be ample to drive a Celeron 700 and 2 HDDs, but definitely worth investigating. So I disconnected one drive entirely and removed absolutely everything I could from the PC, even the PCI NIC (apparently these can use about 4W). My assumption is that Dell wasn't cutting it too fine with their original specs and, since I'm using less components than their original design (no CDROM, and even the PCI riser removed) it should be within tolerance (although the 300GB HDD in there probably uses more power than the original 6G or whatever would have shipped with it). Clicking still present, although this admittedly this isn't a fully reliable test.
@fordem: That was kind of my thinking, also. Drives certainly spin up OK and spin down fine when I get NASlite+ to terminate, and there's no problems with accessing one or more drives simultaneously from clients, so my current (no pun intended!) feeling is that power isn't the issue. But, with a 152W PSU and two big new HDDs, there's a good chance I'm wrong.
I do have a lingering suspicion that it is SMART-related, even though I have this disabled in NASlite+. I have doubts because of the big disk churn that happens at startup, which I've read on these forums is caused by SMART, is that right? If it is, and yet I've got SMART disabled, why does it still do this checking (or whatever it does)? So if SMART is somehow still doing something then maybe it is also causing this drive head-stirring that is resulting in the drive clicking?
I also found a reference to
a similar problem, which seems to suggest power management in the OS. Is there any way for me to implement these commands (I can't see how to get a command shell from within NASlite, and I'm guessing there probably isn't one?)?
As another thought, do people think it might be worth my moving to NASlite 2? Is there some improvements in that version that may help this issue? And is there a limited-time trial version of v2 that I could test? Or perhaps there are other enhancements in v2 over v1.5 that make it a worthwhile move anyway?
Apologies for all the questions! I figure it's a good way to learn a bit about how NASlite+ works even if I can't resolve the issue, so I do appreciate everyone's time on this.
CJ