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Recently I had a discussion with a teacher of mine. He was claiming that you could set up RAID 1 with five drives and that the data would be mirrored over all of these drives.

I told him a RAID 1 with 5 drives wouldn't work like that. It would be a RAID 1 with two drives and would use the other three drives as hot spare.

He also said that RAID 6 is identical to RAID 5 but you can place all the parity checks on the same drive. I thought RAID 6 was a RAID 5-like solution where two drives where used for parity.

Who's right, then?

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2 Answers

You can use as many drives as you want for RAID1. They will all be mirrored, and written on at the same time, and be exact copies of each other. The fact that there isn't a card that do more than x drives doesn't meant anything about the concept. RAID1 is just mirroring your disks, and you can have as many mirrors as you want.

Also, your view of RAID5/6 is erroneous. The parity is distributed on all the drives, there isn't a dedicated drive for that. Compared to raid5, raid6 adds an additional parity block, which is also distributed.

You can find more info on wikipedia.

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I never had a raid-card that could handle raid 1 with more then 2 drives. so ... And what is wrong with my raid-6??? I was trieing to say that raid-5 has one drive for its parity, and raid-6 has 2 drives for parity. As wikipedia says: RAID 5: Block-level striping with distributed parity. RAID 6: Block-level striping with double distributed parity. –  Mad_piggy Oct 19 '12 at 8:56
    
I'll update my answer. –  m4573r Oct 19 '12 at 9:03
    
I've seen an example of mdadm (linux software raid) using 8 drives in a raid 1, or rather the first small partition on 8 drives as a raid 1. This stored the system drive. The big partition on each drive was than grouped in to a RAID 6 array. I've not seen a linux distro that will boot from a software raid 5 or 6. –  BeowulfNode42 Dec 16 '13 at 12:00
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There are two possibilities:

use

  • all 5 drives for the raid 1, with every drive as exact copy of other drives
  • mirror (example) 3 drives and use the other two disks as spare (if one of the first 3 disks fails, the 4th will take his place)

I prefer the 2nd solution (with 2+1 drives or 3+1)

your assumption about raid 6 is wrong :)

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