Re: Swap space settings and other partitioning q's

From: J.O. Aho (user_at_example.net)
Date: 02/09/05 

Date: Wed, 09 Feb 2005 00:15:39 +0100

Morningdew wrote:

> I was just curious to know... What are some good rules of thumb for
> configuring swap space under Linux? For that matter, are there any
> comprehensive guides or articles on the subject? When I used to admin
> NT boxes I used to set their "virtual memory" setting to 1.5 times
> physical memory, giving 50% over physical as swap. That was just by
> convention, or, "rule of thumb". No great scientific methodology, it is
> just what had worked for me and my coworkers for so long. Granted,
> Linux is different.

Size for swap usually have been given as 1.5 to 2.5 times the size of ram,
everything depending on whom you are talking with and what distro you use. I
have settled for around 2 times the ram size, not that I ever have had more
use than a few MB of the 4GB swap.

> Initially I had set up a 32-bit install on one drive, and a
> 64-bit (AMD64) on the other. I decided to go with my old NT convention
> for grins, and give 50% over physical for swap. But since I have both
> swap partitions available, I have both the 32 and 64 bit installs using
> both swaps, for a nearly 1:1 phys:swap ratio.

One swap is enough, even if you run 32-bit and 64-bit linux, but if you have
heavy usage of swap, then splitting up to more than harddrive can speed the
swap speed.

> One consideration, besides size, is location. This question goes beyond
> swap space, too. How does Linux like to have it's partitions metered
> across multiple drives? Should the root and swap be on different
> physical drives or does it matter? If it is better to separate, which
> would benefit most from "the faster drive"? Does it actually help to
> split the swap amongst partitions on differing drives, similar to (yes,
> remotely similar to) how striping speeds up RAID performance?

Today with the hughe RAM, swap is quite rarely used, so you can put it on
slower harddrives or use the end part of the harddrive. I have always set my
swap as the last slice on my harddrives (usually only one harddrive with swap).
Stripping would speed up swap, but you don't need to setup it as raid, IBM had
a quite good article about swap on linux, but sadly I can't find the right
link at the moment.

> While I am asking, I would also be interested in suggestions with regard
> to partitions and placements. I have been running 5Gb roots that include
> my /var and /home. Most of my "media", including music, video, photos,
> and the like I have been keeping on a separate partition that I mount
> under /mnt/share. This way I have access to it from whichever root I
> boot to, as well as making it publicly readable to my family's logins.
> Not much needs to be kept private, and, well, I manage that when need be.

I have done differently, I have a fileserver where I have setup a LVM, this
one is up on 360GB at the moment (max out at 2TB), the LVM is my /home and I
share it with NFS to all my computers, so login in you will access all your
files and settings, regadles on which computer you happen to work at.
I have only removeble medias mounted in /mnt (cdrw/dvdrw/zip/mp3/floppy).

Otherwise I have /usr, /usr/src, /tmp and / as own slices, on machine with the
mailserver I have /var/spool/mail too as it's own (don't want big mails to
fill /var and that way block the system).

> I think it would be unwise for me to make the /home directories be the
> same between the two installs (32 and 64-bit). But I am intruiged to
> know how far such a notion could be taken. Being able to have
> Thunderbird and my GPG keys available no matter which I boot to would be
> rather convenient. I could spend more time in 64-bit land. Right now I
> must use the 32-bit install for that.

Why would that be the case? The settings would still be the same for the
applications, regadles if they are compiled as 32 or 64 bit, just waist of
space to have more than one /home.

> Lastly, since I don't want to tap you all toooo much all at once, I am
> curious about this whole "chroot" thing. Since I have both 32 and
> 64-bit installs, is there a way to make my 32-bit root BE the chroot
> under 64-bit? That would totally rock! I have zero experience with this
> and am only sort-of understanding how it all works. I would like to,
> for instance, just run 64-bit firefox and have it use 32-bit
> libflashplayer.so. That, of course, being one of the very few things
> keeping me on the 32-bit side 90% of the time when I would much rather
> go 64-bit as much as possible.

I think you may have confused what chroot is, you use it to lock software to
run in a controlled environment.

> But I have heard that you can't have a
> 64-bit app call a 32-bit library. Okay. So then 32-bit FF. But then
> that also means all the dependencies for FF and for FlashPlayer, right?
> Well, then, at what point DO the 64 and 32-bit parts commingle? Would
> 32-bit FF run on the 64-bit X session?

People are running neverwinter nights on 64bits systems, so there shouldn't be
problems, you may need a compat library to allow run 32bit stuff in 64bits
environment, I'm not that much into that as I only have 32bits machines.

  //Aho

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