Date: Fri, 8 Aug 2014 13:54:18 -0400 From: Paul Kraus <paul@kraus-haus.org> To: Scott Bennett <bennett@sdf.org>, FreeBSD Questions !!!! <freebsd-questions@freebsd.org> Cc: freebsd@qeng-ho.org, Trond.Endrestol@fagskolen.gjovik.no Subject: Re: gvinum raid5 vs. ZFS raidz Message-ID: <5B99AAB4-C8CB-45A9-A6F0-1F8B08221917@kraus-haus.org> In-Reply-To: <201408071106.s77B6JCI005742@sdf.org> References: <201408020621.s726LsiA024208@sdf.org> <alpine.BSF.2.11.1408020356250.1128@wonkity.com> <53DCDBE8.8060704@qeng-ho.org> <201408060556.s765uKJA026937@sdf.org> <53E1FF5F.1050500@qeng-ho.org> <201408070831.s778VhJc015365@sdf.org> <alpine.BSF.2.11.1408071034510.64214@mail.fig.ol.no> <201408070936.s779akMv017524@sdf.org> <alpine.BSF.2.11.1408071226020.64214@mail.fig.ol.no> <201408071106.s77B6JCI005742@sdf.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Aug 7, 2014, at 7:06, Scott Bennett <bennett@sdf.org> wrote: > Even just as parity bits, those would amount to only one bit per > eight bytes, which seems inadequate. OTOH, the 520 bytes thing is > tickling something in my memory that I can't quite seem to recover, = and > I don't know (or can't remember) what else those eight bytes might be > used for. In any case, at the time I spoke with the guy at = Seagate/Samsung, > I was unaware of the server grade vs. non-server grade distinction, = so I > didn't know to ask him anything about whether silent errors should be > accepted as "normal" for the server grade of disks. Take a look at the manufacturer data sheets for this drives. All of the = ones that I have looked at over the past ten years have included the = =93uncorrectable error rate=94 and it is generally 1 in 10e-14 for = =93consumer grade drives=94 and 1 in 1e-15 for =93enterprise grade = drives=94. That right there shows the order of magnitude difference in = this error rate between consumer and enterprise drives. The reason no one even discussed it prior to the appearance of 1TB = drives is that over the life of a less than 1TB drive you are = statistically almost assured of NOT running into it. It was still there, = but no one wrote/read enough data over the life of the drive to hit it. On the other hand, I am willing to bet that many of the =93random=94 = systems crashes (and Windows BSOD) were caused by this issue. A hard = disk returned a single bit error in a bad place and the system crashed. Note that all disk drives include some amount of error checking, even as = far back as the 10MB MFM drives of the 1980=92s. Anyone remember having = to manually manage the =93Bad block list=94 ? Those were blocks that = were so bad that the error correction could not fix them. But, as far as = I can tell, the uncorrectable errors have always been with us, we just = did not not see them. -- Paul Kraus paul@kraus-haus.org
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?5B99AAB4-C8CB-45A9-A6F0-1F8B08221917>