On Jun 6, 2007, at 3:28 PM, Phil Thayer wrote:
I didn't think RAID 5 or RAID 6 kept all parity data on any one particular disk. I thought it was spread across all the disks. In the case of RAID 6 I thought that the parity was stored on different disks each time but never both on the same disk.
In any case, I think you both may be right. They are using a different parity algorithm for the second parity to be able to recover from a multiple disk failure which would cause the loss of multiple bits of the data. My bad on that one.
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Luke -Jr Sent: Wednesday, June 06, 2007 12:39 PM To: [email protected] Subject: Re: SATA PT2
On Wednesday 06 June 2007 09:47, Phil Thayer wrote:
As for figuring out the second parity calculation on RAID
6, what the
manufacturers are realizing is that they don't necessarily
have to have
a different parity algorithm to calculate the second parity. Simply putting the same XOR parity data on two separate disks will
provide the
same RAID 6 functionality as having a second parity calculation with lower overhead on controllers. The old KISS methodology is
coming back
into play. I think you will see more and more of the manufacturers going this route.
That only works if one of the dead disks is a parity disk... _______________________________________________ Kclug mailing list [email protected] http://kclug.org/mailman/listinfo/kclug
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No, raid 5 + raid 6 would be of no use if one drive only kept the parity data. Not sure where you got your info. You need to seriously verify your information. RAID 3 has one dedicated disk for parity. Raid 5 has parity across all disks. That is when one disk fails during the rebuild process of a RAID5 array, it will fail. With RAID6, you get recovery when one drive fails, a second will still be able to recover the array. RAID 3 keeps parity info on one disk. Also, have at least 2 drives available for replacement, and have at least 2 backup targets available: via tape, another hard drive all equal to or great than the array. I am amazed at how many people don't understand the current RAID levels.
This is a decent source with creditable sources. http:// www.ecs.umass.edu/ece/koren/architecture/Raid/raidhome.html
A lot of people have no credible information about raid, and "I have experience" is not credible. No telling where they got their information. Using software RAID rather than hardware RAID will affect users' comments. There's a big difference. Now days you want to use PCI-X raid controllers.
If you want performance, don't use parity. If you want redundancy use RAID5+. You should seriously calculate how much your data is worth. If you wish to spend a lot, use both! Sincerely,
William Harrington