From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan *St0fF* Huebner Subject: Re: using dd (or dd_rescue) to salvage array Date: Mon, 06 Feb 2012 22:37:38 +0100 Message-ID: <4F304822.8000102@gmx.net> References: <8eekv8xpcn.ln2@goaway.wombat.san-francisco.ca.us> <0cdtv8xv8f.ln2@goaway.wombat.san-francisco.ca.us> <4F2D7280.8020500@stud.tu-ilmenau.de> <8q0309x4kf.ln2@goaway.wombat.san-francisco.ca.us> Reply-To: st0ff@npl.de Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <8q0309x4kf.ln2@goaway.wombat.san-francisco.ca.us> Sender: linux-raid-owner@vger.kernel.org To: Keith Keller Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 05.02.2012 20:10, Keith Keller wrote: > On 2012-02-04, Stefan /*St0fF*/ H=C3=BCbner wrote: >> actually, ddrescue is THE WAY TO GO in this case. Don't use the old >> ddrescue, but the GNU version. Some distros call it gddrescue, on >> gentoo the old one is called dd-rescue and the gnu-one ddrescue. Ju= st >> check it out: http://www.gnu.org/software/ddrescue/ddrescue.html > Thanks for the advice, Stefan. Frustratingly enough, I will get a > chance to try GNU ddrescue despite my impatience--I originally used > dd_rescue to try to get an image of the failing drive, and while that > succeeded just fine (only lost 8k), the target ended up reporting ECC > errors during the rebuild! So I've taken a new image with ddrescue > to a tested drive (again, losing 8k), and am hoping that it goes bett= er. > (At the moment I'm just attempting a one-spare rebuild, which I'm hop= ing > will go faster than a two-disk build, and therefore report any proble= ms > sooner.) > > I realized after reading my initial post that I wasn't 100% clear wha= t I > was asking. I knew that some sort of dd would work, but I'd only don= e > it before in a filesystem context, and didn't know how mdraid would > react. So I am curious, does anyone know what I might expect when th= e > rebuild gets to the part on the new image where the data was lost? W= ill > it just create a problem on the filesystem, or might something worse > happen? Should I run a check if the rebuild completes successfully? > And will mismatch_cnt get populated by the rebuild, or would I need a > check to expose mismatches? > > --keith > From the logical point of view those lost 8k would create bad data -=20 i.e. a filesystem problem OR simply corrupted data. That depends on=20 which blocks exactly are bad. If you were using lvm it could even be=20 worse, like broken metadata. It would be good if those 8k were "in a row" - that way at max 3=20 fs-blocks (when using 4k fs-blocksize) would be corrupted. If you're=20 lucky, you won't even notice - like me: my system SSD broke down=20 lately. I ddrescued as much as I could, but around 250k are gone. I'm= =20 dual-booting windows and gentoo and I have not yet encountered a proble= m=20 from the missing data. Lucky me... Cheers, Stefan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html