Linked by Thom Holwerda on Mon 18th Jan 2010 16:57 UTC, submitted by wanker90210
Hardware, Embedded Systems ACM's latest journal had an interesting article about RAID which suggested it might be time for triple parity raid. "How much longer will current RAID techniques persevere? The RAID levels were codified in the late 1980s; double-parity RAID, known as RAID-6, is the current standard for high-availability, space-efficient storage. The incredible growth of hard-drive capacities, however, could impose serious limitations on the reliability even of RAID-6 systems. Recent trends in hard drives show that triple-parity RAID must soon become pervasive."
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RE: What about 5-way RAID?
by gilboa on Mon 18th Jan 2010 23:09 UTC in reply to "What about 5-way RAID?"
gilboa
Member since:
2005-07-06

seriously at some point it just makes more sense to standardize on RAID 10 doesn't it?


You're wrong.
A. A theoretical RAID7 running only wastes 3 drives - no matter how many drives you have. (15% in 20 drive array). RAID 10 will -always- waste at-least 50% of the space.
B. RAID7 can reliably survive the loss of 3 drives. RAID 10 can only reliably survive the loss of one drive. If you lose two (a full mirror), you lose everything. (The top level strip set is lost)

- Gilboa

Reply Parent Score: 2

RE[2]: What about 5-way RAID?
by Soulbender on Tue 19th Jan 2010 16:20 in reply to "RE: What about 5-way RAID?"
Soulbender Member since:
2005-08-18

RAID 10 can only reliably survive the loss of one drive.


Uh, no. That's not how RAID 10 works. Since it's a stripe of mirrors you can lose all but one drive in each mirror set. How many actual drives that translates to depends on how many drives are in each mirror set and how many mirror sets you have.

Reply Parent Score: 2

CodeMonkey Member since:
2005-09-22

RAID 10 can only reliably survive the loss of one drive.


Since it's a stripe of mirrors you can lose all but one drive in each mirror set.


Really you're both right. Best case catastrophic loss: You loose 50% of all your drives, but it's only 1 drive out of each mirror so everything is still fine. Worst case catastrophic loss: You loose both drives in a single mirror and the entire striped array is toast. So you could loose up to 50% of the drives and still be okay or you could loose 2 and be screwed.

Reply Parent Score: 2

RE[3]: What about 5-way RAID?
by gilboa on Tue 19th Jan 2010 16:50 in reply to "RE[2]: What about 5-way RAID?"
gilboa Member since:
2005-07-06

"RAID 10 can only reliably survive the loss of one drive.


Uh, no. That's not how RAID 10 works. Since it's a stripe of mirrors you can lose all but one drive in each mirror set. How many actual drives that translates to depends on how many drives are in each mirror set and how many mirror sets you have.
"

A. If you only want to waste 50% of your data, you must use 1:1 mirroring.
A1. As long as your array uses 1:1 mirroring, losing two drives of a certain mirror-set will kill the array.
B. If you use a 1:3 mirroring, your RAID10 will survive a 2 drive failure, but will waste a staggering 66% of the total disk space.

Either way, RAID 6 is far more efficient and/or resilient - let alone a theoretical RAID7.

- Gilboa

Reply Parent Score: 2