[CentOS] 32 or 64 bit (4 gb ram)

Mon Mar 2 17:37:57 UTC 2009
Warren Young <warren at etr-usa.com>

Dnk wrote:
> Is there any real advantage to using 64 bit when I am right at the 4gb  
> ram threshhold? 

Yes, unless you're not turning on swap.  Once you add swap to a system 
with 4 GB of RAM, you need either PAE or 64-bit to actually use the 
swap.  Since 64-bit CPUs became cheap last year, there's no longer a 
good reason to use PAE on a new system, so that means 64-bit.

You can make much the same argument farther down the line....even with 2 
GB RAM and 2 GB swap, 64-bit might be the right configuration choice.

> The machine will just be a backup machie (rsync).

I doubt you'll actually use all that RAM, 64-bit or not.

An rsync-only box should be completely I/O bound.  If it were a choice 
between more RAM and either another disk spindle or a hardware RAID 
card, I'd choose the better disk setup, here.  I assume you will have a 
gigabit Ethernet link...the trick then is to saturate it, which you 
can't do with a single disk, no matter how much RAM you've got, or how 
much 64-bitness you throw at it.  Fail to saturate the network link, and 
you're slowing your backups.

If the rsync box is on the other side of a slow network link, I'd still 
go for a better disk setup over more RAM.  In that particular case, I'd 
be looking at things like hot spares, because it means you're probably 
not always near the server to swap disks when they fail.