On Sat, 30 Jan 2010, John Robinson wrote:
I think the problem is that modern discs haven't got more reliable, but they have got much, much bigger; "modern" 2G discs had a read error rate of 1 bit per 10^14, and current 2T discs have the same, so while on a 2G disc you could read the whole surface of the disc tens of thousands of times before being likely to get a read error, now it's only tens of times. Someone did recently post links to a formal article analysing this subject to this list, but I can't find it :-(
I think the 4k sector size on WD20EARS (for instance) is supposed to add more ECC information but I'm not sure how this will affect the 10^14 error rate. I think the manufacturers need to work a bit more on it, I don't see how these drives can be used in single drive configuration with the current 10^14 value.
I don't have experience with any other drives than the WD20EADS but they develop read errors at a rate higher than any other drive I've experienced before (and I started doing computer stuff in the 80ties). Yes, the large size is absolutely a factor, so the per-block read error rate might not be too high, but the read error per drive is definitely so (and I use the default ubuntu behaviour and read scrub every week).
I'm going RAID6 as soon as I can because of this, I'm tired of this bit-rot when I ddrescue things because of this (hopefully it's just 4k of data in the middle of a file which I care little about).
-- Mikael Abrahamsson email: swmike@xxxxxxxxx -- 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
