Yes. I can't see any way that RAID 1 can be less reliable than a single disk.

In reply to a post by AEP:

Yes. I can't see any way that RAID 1 can be less reliable than a single disk.

Well, if the probability of the controller card failing is higher than the probability of the disk failing, in a 2 disk setup, then in that situation having just a single disk is more reliable, give or take a few factors of course.

Edited by Pipexer (Tue 12-Jul-11 18:45:00)

I don't have figures to hand but, personally, I have never experienced failure of any disk controller card, RAID or otherwise. I have experienced several drive failures. It figures, as a combination of electronics and mechanical parts would be expected to be more prone to failure than pure electronics.

In reply to a post by AEP:

I don't have figures to hand but, personally, I have never experienced failure of any disk controller card, RAID or otherwise. I have experienced several drive failures. It figures, as a combination of electronics and mechanical parts would be expected to be more prone to failure than pure electronics.

I guess it's usually the dicky motherboard versions which can fail (i.e on their own or if other parts of the mobo go pop too), but, I am certain that some controller cards (onboard or not) were and are produced which are more prone to trouble than disks.

Enable your PM briefly and I'll send you an interesting link

Edited by Pipexer (Tue 12-Jul-11 18:53:15)

Enabled.

In an external RAID 1 disc setup, does the controller ensure the data is fully committed to one drive before committing to the other, or does it do them in parallel?

It would seem to me that the former is safer than the latter.

As with others I've never had a drive or controller fail, but there's always a first time...

I believe that most, if not all, controllers write the data in parallel. Sequential writes would impact performance, and I'm not sure that they would be any safer. RAID is really there to protect against hardware failure rather than power loss or filesystem corruption.

Bear in mind that almost all modern file systems are journalled, so writes are essentially atomic. Although not recommended, a power failure rarely seems to corrupt file systems nowadays. Of course, in a critical system you would use a UPS but I wouldn't bother with a backup drive. If it fails halfway through a backup it doesn't really matter; it'll fix itself next time.