Re: [PLUG] swappiness and ssd

Having been ringside for some really intensive and real world testing-to-destruction on SSD over the last year or two, I feel I can very confidently say that concerns about write longevity on current SSDs are overstated by about two orders of magnitude. [1] First failures didn't happen until the hundreds of TB were written, and most drives survived in various fashions to near 1PB or more.

So minimizing writes is good, sure, but I don't think spending a lot of time on it is worthwhile. Better to verify that you have solid backups, taken regularly, and have a replacement/restore plan; particularly as SSD prices have come down, continue to come down, and aren't expected to do anything but continue to drop.

[1] http://techreport.com/review/27909/the-ssd-endurance-experiment-theyre-all-dead

On Mon, Jul 13, 2015 at 11:47 AM, Keith C. Perry <kperry@daotechnologies.com> wrote:

Rich, sounds like K.S. is getting some decent performance...

K.S., I generally run XFS too but have you tried running any other filesystems on your SSD? Swap usage is one thing but the journaling is going to increase the numbers of writes too and I would be worried about that. 'Not sure how to quantify this or if it really matters in a practical sense.

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Keith C. Perry, MS E.E.
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----- Original Message -----
From: "Rich Freeman" <r-plug@thefreemanclan.net>
To: "Philadelphia Linux User's Group Discussion List" <plug@lists.phillylinux.org>
Sent: Sunday, July 12, 2015 3:49:49 PM
Subject: Re: [PLUG] swappiness and ssd

On Sun, Jul 12, 2015 at 10:14 AM, K.S. Bhaskar <bhaskar@bhaskars.com> wrote:
>
> The traditional view of swapping is that it is undesirable because reading
> from swap is slow, and swap should therefore be used only if unavoidable.
> Therefore, the received wisdom is to set a low value of swappiness, to swap
> only when unavoidable, and take a performance hit when that happened.
>
> But, write cycle limits aside, I believe SSDs require a rethink.

I'd be very interested in feedback from those using swap on SSD.
However, I never thought that swapiness=0 was conventional wisdom on
Linux. I can think of a million reasons why a higher setting /should/
be better. The problem is that it often isn't, and that is just due
to limitations in Linux and how it is used. The defaults probably
make running updatedb twice in a row a lot faster, but the problem is
that nobody actually does that, and all that swapping after running it
once kills everything else you do.

It has been a while since I've run with swap, so it is possible that
things have gotten better. I do agree that performance of swap should
be much better on an SSD.

The other thing I'd be concerned with is ssd write cycles. I've tried
to move a lot of my heavy-modification activities off of ssd for this
reason. Swap is going to tend to wear it faster.

--
Rich
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