From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas =?iso-8859-1?Q?Sch=E4fer?= Subject: Re: somewhat OT query on journalling Date: Fri, 21 Jul 2006 23:26:11 +0200 Message-ID: <20060721212611.GA13453@wintermute> References: <20060719152744.GA26155@tranquility.scriptkitchen.com> <44BE95F6.50004@namesys.com> <20060721124518.GA1977@tranquility.scriptkitchen.com> <44C122F1.7000109@slaphack.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="W/nzBZO5zC0uMSeA" Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com Content-Disposition: inline In-Reply-To: <44C122F1.7000109@slaphack.com> List-Id: To: reiserfs-list@namesys.com --W/nzBZO5zC0uMSeA Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable > Don't get too excited -- the transactions probably aren't done yet. Witho= ut those, no filesystem that claims to journal data is really any better th= an a filesystem which only journals metadata. Even once=20 > they are implemented (or even if they are already), applications have to = support them directly. Actually, I think transactions in a filesystem context are a bit different from the transactions you know form databases. Generally speaking, a transaction denotes a transition from one valid state to another. This transition should either be performed completely or -- in case of errors -- performed not at all (a.k.a. "roll back"). Databases allow application defined transactions (i.e. the application specifies when a valid state is being left and when one is reached again). IMHO for filesystems a transaction denotes the flushing of write buffers. "metadata only" transactions/journaling mean that even after a crash the file itself will be readable (and not pointing to e.g. sector -4711 ...). "data _and_ metadata" now means that the filesystem does also guarantee that the data itself is written completely. Please correct my if I got this totally wrong. -Andreas --W/nzBZO5zC0uMSeA Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.4 (GNU/Linux) iD8DBQFEwUZzxQzSAzXqsyYRAjOhAKCO/mCHY1yU2GMdCSZDGTd2a/ngTACgkTsx 9694WvWuo4I4iGKzYUq6FOI= =nCyi -----END PGP SIGNATURE----- --W/nzBZO5zC0uMSeA--