On Fri, Jul 13, 2007 at 04:33:14PM -0500, Matt Dittbenner wrote:
> I've got a server with an "AMD Athlon(tm) 64 Processor 3200+" running 
> Gentoo. Everything has been compiled as 32-bit (i686). I am in the process 
> of looking at a new server from Dell with a 64-bit Intel Processor 
> (currently comparing the Xeon E5310 & the Xeon 5130). Questions are as 
> follows:
>
>   1. If I plan on getting 8GB of RAM, will I need (or really want) to
>      install 64-bit linux? Are there gains by going 64-bit or is it
>      better to enable high ram support in the kernel, compile as 32 and
>      call it done?

It depends.  In 64 bit mode you can access the extra registers, as
well as use the old registers in new ways.  You pay by having larger
code size and larger memory consumption (the pointers double).

Note that Xeon 51xx is the old, power hungry Netburst architecture,
while the 53xx is the new and more efficient Core architecture.  Both
support 64 bit mode, but on the Netburst it is significantly slower
(you pay, but not gain anything).

>   2. Will I be able to use the same binaries from the old server on the
>      new one if I install 64-bit? I'd really prefer to copy as much of
>      the data from the old server to the new one as I can. I am aware
>      that a 64-bit chip can run 32-bit software, but I don't know the
>      details. Do I need a 64-bit kernel? How about libraries?

You can use the same binaries, but you'll have to have two sets of
libraries, thus increasing the memory requirements.  When you have the
same program running in many instances, like a server, the OS keeps
only one copy running in the memory; it is the same with libraries,
but if you have one 32-bit program and one 64-bit program all using
the "same" library, they cannot share the image.

> I realize these questions are probably very generalized, but I have 
> basically zero knowledge of the subject so I don't really even know where 
> to start. If people need more info to be able to answer, I'd be happy to 
> provide it.
>
> Essentially, it comes down to this:
>
> Should I use 8 GB of RAM in a 32-bit machine?

It depends.  What will the machine do?  Do you have a process that can
use that much memory by itself (like a database), or do you have many
smaller processes and you want plenty of cache for the disk I/O?
In the first case, the 64 bit route is much simpler and more efficient
code (less swapping and messing up with switching pages around).  In
the second case, it does not matter much.

On the 32 bits you can access up to 64 GB.

> How much work is it to transition a machine from 32-bit to 64?

For a regular server you should see no extra work.

> I really appreciate all the help TCLUG has been in the past. A good group 
> of solid techies. Thanks.

Feel free to post more detailed questions.

Cheers,
florin

-- 
Bruce Schneier expects the Spanish Inquisition.
      http://geekz.co.uk/schneierfacts/fact/163
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: Digital signature
Url : http://mailman.mn-linux.org/pipermail/tclug-list/attachments/20070713/24ff3af9/attachment.pgp