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

Ross Walker rswwalker at gmail.com
Mon Mar 2 17:53:17 UTC 2009


On Mon, Mar 2, 2009 at 12:37 PM, Warren Young <warren at etr-usa.com> wrote:
> 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.

You can definitely use the 2GB+ on an I/O bound box for disk caching!

A lot of people underestimate the performance benefit of page cached
backed I/O when building out storage boxes.

-Ross


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