NAS RAID failure - recovery?

By tycho1974
Jun 11, 2010
  1. Good morning, everyone. I don't have much experience or knowledge in the world of RAID arrays, and I recently had a power surge that burned my NAS. I have an Intel SS4200-E NAS box with 4 1TB drives set up in a RAID-5. It was running fine, and, having experienced a drive failure event due to my careless handling of the power cord, proved to me its ability to rebuild a drive from the other three.

    Unfortunately, a recent power surge literally burned the box. I've taken it in to get analyzed by some HDD repair & recovery people, but I have no frame of reference for this.

    Story is thus: After the surge, I was able to login to the dashboard app of the box via my network. It reported all drives as failed, and provided no further information. The repair guy is saying that 2 of the 4 drives are fine, while the other 2 have electronic/mechanical failures; in addition, the RAID chip on the NAS box was fried. Those three things have to be repaired in order to even begin drive rebuilding. His quote for repair & recovery was in the vicinity of $3,000.

    My first question is whether or not this is a reasonable price. My second pertains to the Parity structure of the RAID setup. Because the system can lose 1 out of 4 drives and still retain data integrity, is it possible to only repair one of my failed drives and rebuild with those three? I'm thinking that would bring the cost down. And realistically, what percentage of data am I likely to recover?

    I'd appreciate some help on this, as I'm completely in the dark about all of this. Thanks!
  2. jobeard

    jobeard TS Ambassador Posts: 9,145   +597

    one hd is the parity drive; if it's gone - - so are you. sorry
  3. tycho1974

    tycho1974 TS Rookie Topic Starter

    I'm not sure I understand - are you saying that one of the three drives is "special", for lack of a better word? As I stated in my original post, I had an incident where I accidentally unplugged the power to the box and screwed it up. Upon rebooting, one of the drives was listed as "faulted". After a day, however, the system had reformatted the faulted drive, and repropagated the data across all four.
  4. jobeard

    jobeard TS Ambassador Posts: 9,145   +597

    oops; my mistake

    Block-level striping with distributed parity.

    Distributed parity requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive. A single drive failure in the set will result in reduced performance of the entire set until the failed drive has been replaced and rebuilt.
  5. tycho1974

    tycho1974 TS Rookie Topic Starter

    Excellent! So, to my ears, that sounds like the data can be rebuilt with just three drives, am I correct in that assumption?

    To be clear: There are 2 fully-functional drives, and 2 damaged drives. My thinking is that the repair guy can take the 2 good drives and 1 of the damaged drives, repair the damage, and rebuild the data. I'm trying to keep the cost of this down...
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