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 computeruser on Mon 18th Jan 2010 22:11 UTC in reply to "What about 5-way RAID?"
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Lets write an extra copy of every write somewhere....and the cool things with this design is that reads will be TWICE as fast since the data exists in two different places, also its even more secure than RAID7 because you can loose not just 2or3 disks but up to ONE HALF of all your disks and still have your data.

No. You can lose one drive in each pair of mirrors. A two-drive failure will result in data loss if both mirrors in a pair happen to fail. A two-drive failure in standard RAID6 does not result in any data loss.

Assuming 1 TB drives in a 4 TB array, 1E-15 bit error rate: Here are roughly calculated probabilities of data loss during rebuild after a single drive has failed and been replaced:
mirror (8 drives total): .00859
two mirrors (12 drives total): .00007
single parity (5 drives total): .03436
double parity (6 drives total): .00118
triple parity (7 drives total): .00004
quad parity (8 drives total): 1.6E-9

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