Numbers are a funny game. Sure, there is a 1000x increase in the chance of an error occurring *somewhere* on the drive - as we have 1000x more space. What you need to keep in perspective is that although building a 2Tb RAID5 from 3 x 1Tb drives may seem more likely to have problems than a 2Gb RAID5 from 3 x 1Gb drives - however if you build a 2Tb RAID5 from 1Gb drives then you would probably increase the likelihood of a failure to around the same levels. >From what I read of the article, it seems like more of a sales pitch and although it has what seem to be good points, they seem to ignore the fact of scaling. ie which is more likely to fail horribly, 3 x 1Tb drives or 3000 x 1Gb drives or even 300 x 10Gb drives? Data storage always seems to be a minefield of misinformation and sales pitches masked as information - however the best practice is to use RAID to hopefully minimise downtime if a drive fails, but keep a copy of your data elsewhere that you have easy access to if you need it. After this, it doesn't really matter if you have a single drive failure - or even a double drive failure in the case of RAID6. If you have more failures and the array crashes horribly, then theres not much you can do but rebuild and restore. On Tue, 2 Feb 2010 17:46:25 -0500, Greg Freemyer <greg.freemyer@xxxxxxxxx> wrote: > All, > > I think the below is accurate, but please cmiiw or misunderstand. > > === > If your using normal big drives (1TB, etc.) in a raid-5 array, the > general consensus of this list is that it is a bad idea. The reason being > that the sector error rate for a bad sector has not changed with > increasing density. > > So in the days of 1GB drives, the likelihood of a undetected / > repaired bad sector was actually pretty low for the drive as whole. > But for today's 1TB drives, the odds are 1000x worse. ie. 1000x more > sectors with the same basic failure rate per sector. > > So a raid-5 composed of 1TB drives is 1000x more likely to be unable > to rebuild itself after a drive failure than a raid-5 built from 1 GB > drives of yesteryear. Thus the current recommendation is to use raid > 6 with high density drives. > > The good news is that Western Digital is apparently introducing a new > series of drives with an error rate "2 orders of magnitude" better > than the current generation. > > See <http://www.anandtech.com/storage/showdoc.aspx?i=3691&p=1> > > The whole article is good, but this paragraph is what really got my > attention: > > "From a numbers perspective, Western Digital estimates that the use of > 4K sectors will give them an immediate 7%-11% increase in format > efficiency. ECC burst error correction stands to improve by 50%, and > the overall error rate capability improves by 2 orders of magnitude. > In theory these reliability benefits should immediately apply to all > 4K sector drives (making the Advanced Format drives more reliable than > regular drives), but Western Digital is not pushing that idea at this > time." > > So maybe raid-5 will once again be a reasonable choice again in the > future. > > (I think these drives may already be available at least as > engineering samples. Basic linux kernel support went in summer 2009 I > believe. I believe 2.6.33 will be the first kernel to have been tested > with these new class of drives.) > > I don't know if there is a mdraid wiki, but if so and someone wants to > post the above there, please do. > > Greg > -- > Greg Freemyer > -- > 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 -- Steven Haigh Email: netwiz@xxxxxxxxx Web: http://www.crc.id.au Phone: (03) 9001 6090 - 0412 935 897 Fax: (03) 8338 0299 -- 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
