From: Pavel Machek Subject: Re: bcache with existing ext4 filesystem Date: Tue, 25 Jul 2017 22:55:27 +0200 Message-ID: <20170725205526.GA31280@amd> References: <20170724185703.GA31422@amd> <64c810cf-a95c-f862-f25a-ebd7419b2632@thelounge.net> <20170724191548.GA32425@amd> <20170724192718.t7n5zgualz5lillg@thunk.org> <20170724200451.GA4318@amd> <20170725045156.kbyaxj4mmi75yyt5@thunk.org> <20170725134604.GA26445@amd> <20170725180225.2k3o6xtdnhygrhia@thunk.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="DocE+STaALJfprDB" To: Theodore Ts'o , Reindl Harald , linux-ext4@vger.kernel.org, kernel list , kent.overstreet@gmail.com, linux-bcache@vger.kernel.org Return-path: Content-Disposition: inline In-Reply-To: <20170725180225.2k3o6xtdnhygrhia@thunk.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org --DocE+STaALJfprDB Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue 2017-07-25 14:02:25, Theodore Ts'o wrote: > On Tue, Jul 25, 2017 at 03:46:04PM +0200, Pavel Machek wrote: > >=20 > > Is there some field in ext2 superblock that changes every time > > filesystem is changed? Is mtime changed by fsck/badblocks/...? >=20 > No, there isn't. If we were writing the superblock every time the > file system is changed it would be ***extremely*** flash unfriendly. > It would also be a scalability bottleneck, it would cause us to pay an > extra HDD seek, etc. So it's a really bad Bad BAD idea, and so we > don't do it. Ok, I did not mean "every time" when I said "every time". That would be too heavy. I mean... is there something changed by the regular mount (like mtime) plus by operations like fsck and badblocks? In particular, does fsck change mtime when it writes to the filesystem? Thanks, Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --DocE+STaALJfprDB Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAll3sD4ACgkQMOfwapXb+vKXDgCfQFpuErVEMAjgavomMw/yJjIc bNAAnRsdkB1MyQq7JpggFTauTT9DqBi6 =m8za -----END PGP SIGNATURE----- --DocE+STaALJfprDB--