From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: md-raid paranoia mode? Date: Thu, 12 Jun 2014 16:45:07 +1000 Message-ID: <20140612164507.3af9fe1d@notabene.brown> References: <5397FBCE.3060009@bartk.us> <53990D44.300@fnarfbargle.com> <20140612122814.2db74377@natsu> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/yK5jnZDGvD4S3lAw_7JkC02"; protocol="application/pgp-signature" Return-path: In-Reply-To: <20140612122814.2db74377@natsu> Sender: linux-raid-owner@vger.kernel.org To: Roman Mamedov Cc: Brad Campbell , Bart Kus , linux-raid@vger.kernel.org List-Id: linux-raid.ids --Sig_/yK5jnZDGvD4S3lAw_7JkC02 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Thu, 12 Jun 2014 12:28:14 +0600 Roman Mamedov wrote: > On Thu, 12 Jun 2014 10:15:32 +0800 > Brad Campbell wrote: >=20 > > On 11/06/14 14:48, Bart Kus wrote: > > > Hello, > > > > > > As far as I understand, md-raid relies on the underlying devices to > > > inform it of IO errors before it'll seek redundant/parity data to > > > fulfill the read request. I have, however, seen certain hard drives > > > report successful reads while returning garbage data. > >=20 > > If you have drives that return garbage as valid data then you have far= =20 > > greater problems than what you are suggesting will fix. So much so I=20 > > suggest you document these instances and start banging a drum announcin= g=20 > > them in a name and shame campaign. That sort of behavior from storage=20 > > devices is never ok, and the manufacturer needs to know that. >=20 > If your RAM can return garbage, that's not a justification for having ECC= RAM. > ECC RAM is a gimmick invented by weak conformist people. Instead, you sho= uld go > and loudly scream at the manufacturer who sold you that RAM! Errors from = RAM > are never OK! RAM should always work perfectly! And if it doesn't, you ha= ve > greater problems. We shall not tolerate this behavior! So go get a drum a= nd > start banging it as loudly as you can! Name and shame the manufacturer who > sold you that RAM. Fight the power, brother!!! Your screwdriver is leaking (*). Hard drives contain ECC. It should ensure undetected errors are an *extremely* rare event (more rare than bugs in the md code). If your ECC RAM started returning bad data without telling you, would you build a complex virtual memory system to load every byte from two different DIMMs into CPU registers and compare them before trusting them? I know that hard drives can return bad data. I've seen it happen. I don't think that trying to "fix" it in the md/raid layer is appropriate. File-systems and higher level data management systems (e.g. git) are much better placed to detect such errors than md/raid is. Supposedly btrfs will DTRT with your drives (though TRT is to RMA them, and I don't think btrfs has an RMA plugin yet). >=20 > You can probably tell just how sick I am of reasoning like yours. That's = why > we can't have nice things (md-side resiliency for the cases when you need= /want > it), and sadly Neil is of the same opinion as you. >=20 In general, if you want nice things you need to pay for them. If you are willing to pay I suspect you can find someone who is willing to provide. NeilBrown (*)http://www.zazzle.com/a_bad_analogy_is_like_a_leaky_screwdriver_tshirts-= 235102919981826183 --Sig_/yK5jnZDGvD4S3lAw_7JkC02 Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQIVAwUBU5lMcznsnt1WYoG5AQJCGg/+KpmgxJfez7PES3Oe8Grj4Rn0Mc+KuZdi jF4p2Ly6K3eDV0xcLwqAUCRoF5t1zCvuKki9JxmJOyC8YtvlXH9Z87PYZnzyvPy3 l9MtNrmkdVmTE7LNawuHRhevtz/lZyAN2dCRY4gvryKK38KZaUyKk5hVHIy8nU82 qDvNkiyJI56COL52gKv7duR6lfgUufkTRRsUXESU0VZX9/nFoRCqTSlQQDaHgIIh vGqbBS1jv03umIUvHJSl/Ifbgs+zCzkM1L99wtzuNZ8LWg61l9F7n1fCMHIf15Ie T/0xO/onq+l+9T7Q2siggwLtvBV+O/pT4l/RbpAQBIq8/OS17+cJtyXNPX791s5G C2hZkJUPGYiqe/n0zLSgOU+Vr9ITtam7JgMoMbIlwdtiYVBqgEmjqxBkSrGxV1Kk /omI9gXHztLeCl8Zlu3+IpujfJx+RVWx1lWE78YOCjFa4EVUlBivo/2rzKf/GZWi b79ymNDsbsYXwdC+iKYUdPW7Rqjpiob2F1yXf+4UQaVFwj+OKUMMcYsUsWzOMyJV nn+MJY0HPde5Pv7i8RxPLV8xzX8VKmpeO96GEnAXYHnS2ZZ7mx2FAIESucKmA7f8 mGiuZ9SQYfsoHHBHkZNKnC/vtZ35vGVZ5xw4llfZ+2cfpxkHzyTbKaJmbwiv7QjY /MABMGcaX8s= =PruA -----END PGP SIGNATURE----- --Sig_/yK5jnZDGvD4S3lAw_7JkC02--