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Subject: Re: Why is SU+J undesirable on SSDs?
From: Ian Lepore <freebsd@damnhippie.dyndns.org>
To: Adam Vande More <amvandemore@gmail.com>
In-Reply-To: <CA+tpaK2z7LPG3_ys17RYcs8fefC=o=xM5GSEcze_gCZ8qoBWxw@mail.gmail.com>
References: <201211032130.PAA04484@lariat.net>
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Date: Sat, 03 Nov 2012 16:54:29 -0600
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Cc: Brett Glass <brett@lariat.net>, stable@freebsd.org
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On Sat, 2012-11-03 at 17:06 -0500, Adam Vande More wrote:
> On Sat, Nov 3, 2012 at 4:30 PM, Brett Glass <brett@lariat.net> wrote:
> 
> > Have been following the thread related to SU+J, and am wondering: why is it
> > considered to be undesirable on SSDs (assuming that they have good wear
> > leveling)?
> 
> 
> Superstition
> 
> 

Yeah, that's what it must be.  Or... it could be well-informed choice.

Journaling increases the number of writes.  That puts wear on any disk,
mechanical or SSD, and it takes time.  What it buys you is better
performance if you get into a crash recovery situation.  It's perfectly
reasonable for someone to make the decision that their SSD can finish an
fsck so fast that there's no point in paying any penalty for the extra
writes for journaling.  

I have a 256G SSD here with about 200G of data on it, and fsck without
journaling takes about 3 minutes.  I can live with that.  With more data
or a slower drive I might make a different choice.

-- Ian