From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f169.google.com ([209.85.213.169]:33578 "EHLO mail-ig0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753431AbbLBOcJ (ORCPT ); Wed, 2 Dec 2015 09:32:09 -0500 Received: by igcmv3 with SMTP id mv3so118675528igc.0 for ; Wed, 02 Dec 2015 06:32:08 -0800 (PST) Subject: Re: utils version and convert crash To: Duncan <1i5t5.duncan@cox.net>, linux-btrfs@vger.kernel.org References: <565E0356.9030006@gmail.com> <565EE329.3050902@gmail.com> From: Austin S Hemmelgarn Message-ID: <565F00E0.6040204@gmail.com> Date: Wed, 2 Dec 2015 09:32:00 -0500 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms020404070701080705030502" Sender: linux-btrfs-owner@vger.kernel.org List-ID: This is a cryptographically signed message in MIME format. --------------ms020404070701080705030502 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-12-02 08:45, Duncan wrote: > Austin S Hemmelgarn posted on Wed, 02 Dec 2015 07:25:13 -0500 as > excerpted: > >> On 2015-12-02 05:01, Duncan wrote: > > [on unverified errors returned by scrub] >>> >>> Unverified errors are, I believe[1], errors where a metadata block >>> holding checksums itself has an error, so the blocks its checksums in= >>> turn covered are not checksum-verified. >>> >>> What that means in practice is that once the first metadata block err= or >>> has been corrected in a first scrub run, a second scrub run can now >>> check the blocks that were recorded as unverified errors in the first= >>> run, potentially finding and hopefully fixing additional errors[.] > >>> --- >>> [1] I'm not a dev and am not absolutely sure of the technical accurac= y >>> of this description, but from an admin's viewpoint it seems to be >>> correct at least in practice, based on the fact that further scrubs a= s >>> long as there were unverified errors often did find additional errors= , >>> while once the unverified count dropped to zero and the last read >>> errors were corrected, further scrubs turned up no further errors. >>> >> AFAICT from reading the code, that is a correct assessment. It would = be >> kind of nice though if there was some way to tell scrub to recheck up = to >> X many times if there are unverified errors... > > Yes. For me as explained it wasn't that big a deal as another scrub wa= s > another minute or less, but definitely on terabyte-scale filesystems on= > spinning rust, where scrubs take hours, having scrub be able to > automatically track just the corrected errors along with their > unverifieds, and rescan just those, should only take a matter of a few > minutes more, while a full rescan of /everything/ would take the same > number of hours yet again... and again if there's a third scan required= , > etc. > > I'd say just make it automatic on corrected metadata errors as I can't > think of a reason people wouldn't want it, given the time it would save= > over rerunning a full scrub over and over again, but making it an optio= n > would be fine with me too. > I was thinking an option to do a full re-scrub, but having an automatic=20 reparse of the metadata in a fixed metadata block would be a lot more=20 efficient that what I was thinking :) --------------ms020404070701080705030502 Content-Type: application/pkcs7-signature; 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