From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: If your using large Sata drives in raid 5/6 .... Date: Fri, 05 Feb 2010 16:59:43 +0000 Message-ID: <4B6C4E7F.2080501@anonymous.org.uk> References: <87f94c371002021440o3b30414bk3a7ccf9d2fa9b8af@mail.gmail.com> <87f94c371002021446y38dce6fds6acca2b4919ad773@mail.gmail.com> <4B698365.1040007@anonymous.org.uk> <4B6C3B7D.2090502@tmr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4B6C3B7D.2090502@tmr.com> Sender: linux-raid-owner@vger.kernel.org To: Linux RAID List-Id: linux-raid.ids On 05/02/2010 15:38, Bill Davidsen wrote: > John Robinson wrote: [...] >> What sums I've done, on the basis of a 1 in 10^15 bit unrecoverable >> error rate, suggest you've a 1 in 63 chance of getting an >> uncorrectable error while reading the whole surface of their 2TB disc. >> Read the whole disc 44 times and you've a 50/50 chance of hitting an >> uncorrectable error. >> > Rethink that, virtually all errors happen during write, reading is > non-destructive, in terms of what's on the drive. So it's valid after > write or it isn't, but having been written correctly, other than > failures in the media (including mechanical parts) or electronics, the > chances of "going bad" are probably vanishingly small. They're quite small, at 1 in 10^15 bits read. On 1GB discs, you probably could call it vanishingly small. But now with 1TB and larger discs, I wouldn't characterise it as vanishingly small. It's entirely on the basis of the given specs that I did my calculations. Bear in mind that the operation of the disc is now deliberately designed to use ECC all the time. Have a look at the vast numbers you get from the SMART data for ECC errors corrected. I just checked a 160GB single-platter disc with 4500 power-on hours; it quotes 200,000,000 hardware ECC errors recovered. Cheers, John.