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Date:      Wed, 21 Oct 2015 09:15:33 -0500
From:      Adam Vande More <amvandemore@gmail.com>
To:        "Brandon J. Wandersee" <brandon.wandersee@gmail.com>
Cc:        krad <kraduk@gmail.com>, FreeBSD Questions <freebsd-questions@freebsd.org>
Subject:   Re: gjournal and TRIM: A safe combination?
Message-ID:  <CA%2BtpaK0ezoi7wBBD9VZwREq9Qp0YaJNfJY42=tZAYi5VSL8rCA@mail.gmail.com>
In-Reply-To: <86pp081glq.fsf@WorkBox.Home>
References:  <867fmh12nq.fsf@WorkBox.Home> <CALfReyfg-71nCg4K0dKmUK-YmZ8yi0ppeGGv4WOD-2Mt8NP9HQ@mail.gmail.com> <86pp081glq.fsf@WorkBox.Home>

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On Wed, Oct 21, 2015 at 8:44 AM, Brandon J. Wandersee <
brandon.wandersee@gmail.com> wrote:

> I thought the opposite, myself. `gjournal` has its own section in the
> Handbook, while SU+J isn't even mentioned.


Unfortunately, this is not a safe assumption.  The handbook is maintained
by volunteers.  The volunteers generally do a pretty good job, but are a
few negatives of this approach.  They aren't generally interested in
updating old documentation which doesn't directly apply to them.  The
provided documentation is how they think it should be done: right, wrong or
somewhere in-between.

A lot of things don't get the attention they deserve like SU+J, GELI over
GBDE, and in-kernel NAT w/ FreeBSD single native firewall ipfw.



> I also thought there was
> something fundamentally different about them--like SU+J simply maintains
> filesystem integrity, while gjournal actually protects files from the
> write hole as well as protecting the filesystem. I could be wrong.
>

There is a fundamental difference between them.  Don't you think you should
investigate the differences prior to deciding what to use?

It's not at clear what your goal is here.  Do you want to minimize writes
to the ssd or do you want to ensure the fs is always consistent from both a
meta-data and data perspective.  These options are mutually exclusive in
the parameters you've laid out.

-- 
Adam



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