On Sat, 02 Aug 2014 18:21:07 +0200 Gionatan Danti <g.danti@xxxxxxxxxx> wrote: > Hi again, > I started a little experiment regarding BER/UREs and I wish to have an > informed feedback. > > As I had a spare 500 GB Seagate Barracuda 7200.12 (BER 10^14 max: > http://www.seagate.com/staticfiles/support/disc/manuals/desktop/Barracuda%207200.12/100529369e.pdf), > I started to read it continuously with the following shell command: dd > if=/dev/sdb of=/dev/null bs=8M iflag=direct > > The drive was used as a member of a RAID10 set on one of my test > machines, so I assume its platters are full of pseudo-random data. At > 100 MB/s, I am now at about 15 TB read from it and I don't see any > problem reported by the kernel. > > Some questions: > 1) I should try in different / harder mode to generate UREs? Maybe using > some pre-determined pseudo-random string and then comparing the results > (I think this is more appropriate to catch silent data corruption, by > the way)? You are very unlikely to see UREs just be reading the drive over and over a again. You easily do that for years and not get an error. Or maybe you got one just then. > 2) how UREs should be visible? Via error reporting through dmesg? If you want to see how the system responds when it hits a URE, you can use the hdparm command and the "--make-bad-sector" option. There is also a "--repair-sector" option which will (hopefully) repair the sector when you are done. NeilBrown > > Thanks. > > Il 2014-07-31 09:16 Gionatan Danti ha scritto: > >> Yes, you can usually get your data back with mdadm. > >> > >> With latest code, a URE during recovery will cause a bad-block to be > >> recorded > >> on the recovered device, and recovery will continue. You end up with > >> a > >> working array that has a few unreadable blocks on it. > >> > >> NeilBrown > > > > This is very good news :) > > I case of parity RAID I assume the entire stripe is marked as bad, but > > with mirror (eg: RAID10) only a single block (often 512B) is marked > > bad on the recovered device, right? > > > > From what mdadm/kernel version the new behavior is implemented? Maybe > > the software RAID on my CentOS 6.5 is stronger then expected ;) > > > > Regards. >
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