Disk I/O as a bottleneck?

[is123 at zahav.net.il]

On Sun, 08 May 2011 07:28:49 +0300
Nadav Har'El <nyh at math.technion.ac.il> wrote:

> Instead of buying a huge SSD for "thousands of dollars" another option you
> might consider is to buy a relatively small SSD with just enough space to
> hold your "/" partition and swap space. Even 20 G may be enough.
> The rest of your disk - holding your source code, photos, songs, movies,
> or whatever you typically fill a terabyte with, will be a normal, cheap,
> hard disk.

I don't agree with this setup. Regular consumer drives setup with RAID to
stripe are going to be much, much faster and have less problems in the long
run than single SSDs at this point as well as being a better value until
prices change a lot.

Consider not using swap, because swap when in use causes a lot of thrashing
and kills performance especially if you only have 1 or 2 drives. If you have
a reasonably fast CPU (as the OP wrote) and more than 1G of RAM you can live
without swap. Try it and like it:

/sbin/swapoff -a

Run for a few days and see if your performance doesn't improve.

The only problem I can think of is if you run leaky code and don't have
swap your system will lock up sooner. If you do have swap perhaps you will
be able to see it coming.

Another thing to consider is what filesystem(s) you use and what your
mountpoints are. That's a religious debate and I'm not going to get into it
except to say different filesystems have different advantages and
disadvantages and it's worthwhile to do a bit of research to see which
one(s) will work for you. You might consider one filesystem for volatile
directories like /tmp and /var/log and others for relatively static
filesystems like /. You should also consider your whole filesystem
structure and the way you have mountpoints set up. If you have one big
filesystem for everything (common but incorrect desktop config) you are not
going to get the best performance possible.