On Wed, Feb 16, 2011 at 08:40, Lasse Jensen <fafler@xxxxxxxxx> wrote: > Is a RAID 6 array made by upgrading a RAID 5 array to RAID 6 in any > way inferior to a RAID 6 array build from scratch? I read somewhere > that the last drive would be parity only. I'm not sure what to make of > it and i cant find the link again either. Is it going to be a > bottleneck like in RAID 4? > That information is incomplete or out-of-date. During a RAID 5 to RAID 6 reshape, there may be an intermediate step where all of the Q parity blocks are stored on one disk, but as the reshape continues, it will move all the Q parity blocks to a normal RAID 6 layout. IIRC, in the very early stages of RAID 5 to RAID 6 reshape development, it would leave it in the abnormal layout, but that has not been the case for quite some time. And I believe in some cases a RAID 5 to RAID 6 reshape will not even use the intermediate step w/ the abnormal layout. After the reshape fully completes, it is exactly the same as a RAID 6 array built from scratch. > The story is i have a degraded RAID 6 array with 3 out of 5 drives > active because of random read errors on the drives. Danm you, Western > Digital. Anyway, i can get all my data out, so no worries. I need to > ship the two drives for replacement and when i get them back, i'm > going to rearrange the array to put the encryption layer on top of the > RAID layer instead of the other way around as it drops out drives from > the array from time to time. Thats a whole different story. > > Now, when i get the drives back, i could use one drive for most of my > data and put the rest on a couple of laptops and spare drives, build a > 4 drive RAID 6 array and then add the last drive to the array. > Or i could put my data on two drives a make a 3 drive RAID 5 array, > copy data in to it, add the last two drives and upgrade to RAID 6. > Which is better? > If I understand you correctly, I think the RAID 6 route would be slightly better, because it would have enough parity info to recover from a single drive failure, while the RAID 5 route you describe would lose the array completely if a drive failed before you added the last two drives. Good luck! -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
