[CLUE-Tech] RAID-5

[Roger Frank]

I picked up a hardware RAID controller and three 9.1G SCSI drives 
and cabled it all together.  The controller suggested RAID-5 
when I went into the setup utility.  I set it up for RAID-5 and
installed Linux (using the megaraid SCSI controoler module).
It's running great, and bonnie++ indicated that it's really
running RAID-5.

My question is: what if I get a disk failure?  The excellent
writeup on RAID-5 at http://www.acnc.com/04_01_05.html says
"Disk failure has a medium impact on throughput."  Seems
to me if a disk fails, it's all over.  It only uses parity,
and parity can't tell you how to fix bad data, only that
some bit is incorrect.

So maybe I should use RAID-1?  That is with mirroring and
duplexing.  But even there if I get a disk starting to fail,
the controller won't know who to believe, just that the two
disks disagree.

Also, if the controller is fixing things on one disk, how can 
I find out and perhaps replace the degrading disk?  Is there
a raidtools that knows about hardware controllers?

-- 
Roger Frank                                        rfrank at rfrank.net   
http://www.rfrank.net        Ponderosa High School, Parker, Colorado