On 30/11/12 10:28, Mark Rogers wrote:
We do already have a UPS although I'm not sure it's suitably sized - that's one of the things on my list. I'm pretty sure it's not currently being monitored (historic reasons - the kit that used to monitor it has now gone) which makes it only slightly better than no UPS at all, and I am sure it needs new batteries. Up until now it wasn't powering anything that mattered so that wasn't a big deal.
Assuming I can get to a point where the UPS will keep the server running for a few minutes, and notify it to shut down, then is write caching on the external RAID array "safe"?
If the UPS is monitored, detects a power failure, and initiates a shutdown, I would expect the O/S would request the backup program to terminate, and then kill it if it didn't respond quickly enough. The backup program will stop writing because it's been shut down, and I'm sure the o/s will flush its own write cache to disk before terminating.
I'm reasonably sure that any hardware disk cache will get written to disk before the power is removed so I think you'll be OK.
A monitored UPS at least gives you the chance to attempt to shutdown gracefully, which an un-monitored one doesn't.
Steve
Steve