I've read that a UPS is recommended with a raid configuration but I'm not sure why.

when the power goes off - with a single drive you lose any data that is being written to disc but files on the disc are intact.

with a raid configuration surely its' the same, even if the data is spread over 3 or 4 drives you would still only lose any files currently being written to disc

or am I wrong?

Heads crashing into platters would be one good reason.

A UPS should be used for *any* system and it's mission-critical components to protect against power failure. The main CPU, main monitor, RAID enclosures you name it. If you don't use one it's like not wearing a seatbelt; it's not a question of *if* you'll have a power outage it's when. It's cheap insurance - get one and rest easy.

As well, a UPS provides "top up" benefits for brownouts when voltage drops but doesn't completely blackout.

My UPS reported 167 "events" in a year and a half at my old home and zero so far in the past 8 weeks since it has been online in Vancouver.

Paul... If the file being written to the disc happens to be the directory, then it'll really mess things up on both drives.

As others have said, if it's important, protect it.

A hundred bucks is cheap compared to the potential of losing hours of hard work, and the additional hours it would take to get it all back working again.

I got a Tripp Lite recently from Costco to replace an aging UPS.

A UPS is REALLY good cheap way to cure poor AC quality.

All of the above are true provided the UPS has automatic voltage regulation and you're truly running off the battery at all times. Cheap UPS units are auto switching and the battery only comes online in the case of a power outage. They don't handle brownouts and may not clamp an instantaneous voltage spike. You get what you pay for.

bad power here, a massive amount of construction tapping into the local power lines. i had sudden shut downs, usb thumb drive ejects, non starts, usb audio preamp and monitoring device that would unmount and I'd need to plug in again. Funny, NEVER had a blackout here, or really even noticeable brown outs, but the power is crap.

I have a cheap APC 650 UPS, cured all the above problems, doesn't work on battery but been fine.

I have a cheap APC 650 UPS, cured all the above problems, doesn't work on battery but been fine.

Same reason I have UPS on all my electronics. Not for if there is a blackout, but just because a little power conditioning goes a long way to keeping happy gear.

I've read that a UPS is recommended with a raid configuration but I'm not sure why.

It would also depend on the raid configuration.

If the drives are striped (raid 0) and something bad happens all the drives will be affected. Even if the drives are mirrored (raid 1) they could all have corrupted data written to both disks. Most of these raid setups will protect you in the case that you have a drive failure, but not against power outages and corrupted data written to the discs.

UPS is a good idea.