Mailinglist Archive: opensuse (933 mails)

[Adam Tauno Williams <awilliam@xxxxxxxxxxxxx>]

On Tue, 2010-06-01 at 14:04 +0200, C wrote:
> On Tue, Jun 1, 2010 at 13:53, Adam Tauno Williams wrote:
> > > This is one of those conflicts of information I see.  Some people say
> > > it's a default so no worries.. then the next says.. no way, you have
> > > to set this option or... the world will end... or your SSD will
> > > fail... whichever comes first.
> > The world will end - the question is just "when?" :)
> Or, it's already ended and no one noticed :-)

Possibly several times over.

> > There is no harm in using the noatime setting;  I've been using noatime
> > on all my production servers and my own laptop/workstation for years
> > with no problem.  No modern application cares about atime and it isn't
> > even useful for auditing.
> Hmmm I think it's time for me to read up more on atime.  I need to
> understand it better.

<https://lwn.net/Articles/244830/>
<https://lwn.net/Articles/244829/>

<quote>
i cannot over-emphasise how much of a deal it is in practice. Atime 
updates are by far the biggest IO performance deficiency that Linux has 
today. Getting rid of atime updates would give us more everyday Linux 
performance than all the pagecache speedups of the past 10 years, 
_combined_.
</quote>

This is true.

If they had atime, and a slow I/O bus, and then they set noatime
[because they thought they should on an SSD] - that might explain some
of the performance improvement.

> > Really?  I've seen demonstrations of that and not been impressed.  You
> > could get, IMNSHO, a bigger performance boost by spending that same
> > amount of money on a lot more RAM.  I've got spinning disks and 6GB of
> > RAM and apps start pretty close to instantly.  An order-of-magnitude
> > difference I doubt would even be noticeable.
> That's the bit that is confusing me.  I've seen uber fast startup,

I've no doubt start-up times are faster,  that I'd suspect, would be a
real-world difference.  As for me, start-up is pretty fast anyway, I
don't startup that often (twice a day?)... so I just don't get what the
big deal is.  Faster is nice, but really [for me anyway] it doesn't
matter.

> too).  Then I go somewhere else in my random searches, and the next
> discussion or comment is essentially the same as yours.... benchmarks
> show there is essentially zero difference.

Yep.

>  I wonder, are those
> benchmarks on the cheapy drives (which are def slower) or the higher
> priced and faster drives?

For good SSD's there is a real difference when you are doing a high rate
of *random* and *small* read/writes.  Like with an RDBMS, especially for
a database journal/log partition.

Sifting the good from the lame is arduous work and best left to
experienced testers.

As for normal file-system access - which is mostly big-block reads...
I've seen nothing convincing.  Once the systems cache is filled the
benefit evaporates [so initial booting *is* certainly faster, and then
you also have many services spinning up at once].  But once you are
logged in and working,  just about everything you want should be at
least partially in RAM already.

> > If you believe that is true then it makes sense to use SSD.
> I want to believe... oh wait, that's X-Files.  I'm still undecided
> about the SSD performance... the comments here have been...
> interesting.  I still have time to research it :-)

-- 
Adam Tauno Williams <awilliam@xxxxxxxxxxxxx> LPIC-1, Novell CLA
<http://www.whitemiceconsulting.com>
OpenGroupware, Cyrus IMAPd, Postfix, OpenLDAP, Samba

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