Date: Thu, 22 Oct 2015 09:32:02 -0500 From: Adam Vande More <amvandemore@gmail.com> To: Julien Cigar <jcigar@ulb.ac.be> Cc: "Brandon J. Wandersee" <brandon.wandersee@gmail.com>, FreeBSD Questions <freebsd-questions@freebsd.org>, krad <kraduk@gmail.com> Subject: Re: gjournal and TRIM: A safe combination? Message-ID: <CA%2BtpaK3TRic%2BnTemvCk7iJCb3Fgj7MyAoc9rtEgh_hm=c5oyHw@mail.gmail.com> In-Reply-To: <20151022131510.GY87605@mordor.lan> References: <867fmh12nq.fsf@WorkBox.Home> <CALfReyfg-71nCg4K0dKmUK-YmZ8yi0ppeGGv4WOD-2Mt8NP9HQ@mail.gmail.com> <86pp081glq.fsf@WorkBox.Home> <CA%2BtpaK0ezoi7wBBD9VZwREq9Qp0YaJNfJY42=tZAYi5VSL8rCA@mail.gmail.com> <20151021143525.GX87605@mordor.lan> <86lhaw107r.fsf@WorkBox.Home> <20151022131510.GY87605@mordor.lan>
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On Thu, Oct 22, 2015 at 8:15 AM, Julien Cigar <jcigar@ulb.ac.be> wrote: > On Wed, Oct 21, 2015 at 02:38:16PM -0500, Brandon J. Wandersee wrote: > > > > Julien Cigar writes: > > > Correct me if I'm wrong but, unless there is a bug in Soft Updates > (SU), > > > your FS will, in theory, never be corrupted with SU only. > > > > If I read this right, then, would gjournal be overkill for typical > > desktop/laptop use? UFS2 is perhaps the only filesystems I've ever > > encountered in common use that doesn't have data journaling enabled by > > default, so that's thrown me off somewhat... > > It depends of your needs, but for a typicaly desktop use it seems a bit > overkill to me. > > Contrary to other filesystems UFS doesn't need journaling to avoid > _corruption_ as SU is an alternate approach to maintain metadata > integrity. > > One important thing to remember is that neither SU, or SU+J, or any > journaled metadata prevents data loss: corruption != data loss. This is > where gjournal (and data=journal on EXT-like FS) comes in as datas and > metadatas are written in the journal _before_, so you avoid corruption > and data loss. > gjournal nor data=journal nor COW prevent data loss. They simply ensure both meta-data and data are consistent. In general though they do reduce the risk of data loss at a high cost in journaled scenarios. -- Adam
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