[lug] RAID redundancy with boot sectors?

Nate Duehr nate at natetech.com
Sun Nov 26 20:05:04 MST 2006

David L. Anselmi wrote:

> So for me RAID shortens the critical path by at least half, and takes 
> away the pressure during the troubleshooting and fixing parts.  To me 
> that's worth it (like you said, playing with software RAID is fun anyway).

Sounds like you've done the analysis and made the right choice for you. 
   That's good.

>> So for non-critical machines where "Real" RAID can't be purchased, you 
>> end up no worse off to buy a pair of cheap bigger drives, reload,
>> and restore backups... and now you have three drives (one smaller
>> than the other two) and you usually didn't take that much more
>> downtime than messing around rebuilding the software RAID.
> The time difference might be smaller if the second drive is sitting on 
> the shelf waiting to be installed.  But you don't really want to have to 
> buy a new drive while the machine is down, if people aren't able to work.

Yeah, I generally find that "people can't work" machines can almost 
always create enough "nervousness" about downtime that really good 
hardware can be afforded.  The more money the machine makes or saves, 
the more money is available to buy it appropriate hardware.

> I don't necessarily think real RAID is better:
> In one office, motherboard failures beat drive failures 4 to 1.  Of 
> course that's an outlier.

Wow!  Would you believe (and this may be an out-lier too ... out-liar? 
heh...) that I've never had a motherboard failure since I started using 
computers in 1982?  Not one that I didn't directly cause by plugging 
something in wrong and blowing it up, anyway... basic electronics.  :-)

> In another office the RAID controller was a single point of failure and 
> it failed before any of the drives.  The complexity of the recovery 
> resulted in losing the on-disk data requiring restore from tape.

Ouch.  Hadn't though to consider the controller itself.  Ugly.

> At that same office kicking the plug out of a RAID resulted in losing 
> all the on disk data.

Um, OUCH!  Hopefully they learned the lesson of physical security for 
servers?  Whew.

> Granted my experience is somewhat peculiar.  But RAID assumes the drives 
> will fail first.  After you account for single points of failure and the 
> complexity of a RAID setup you might not have gained any reliability. 
> It's still a useful tool in the right hands but I've seen it used badly 
> too often.

My experience has been the drives fail, and little else does -- but 
maybe my experience is the bad one.  :-)


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