Value of memory

[Fajar A. Nugraha]

On Thu, Aug 7, 2014 at 10:39 AM, Robert Moskowitz <rgm at htt-consult.com> wrote:
> I have a server that is only running bind 9.8.2 (Centos 6.5).  It has 2Gb
> memory and free reports ~1.7Gb used.
>
> I am looking at replacing this server with an armv7 board running Redsleeve
> (until Centos 7 is out and stable for armv7).  I have a choice of boards,
> one with 1Gb memory ($60) and one with 2Gb memory ($90).
>
> This server servers out my zones and supports the couple handfull of systems
> on my net.  I would like to eventually get to DNSSEC, but that is another
> stalled project.
>
> About the only meaningful difference between the two boards (btw,
> Cubieboard2 and Cubietruck) for my needs is the memory.  I know more memory
> is better, but how much better?
>
> Oh, why the move to arm?  Power consumption.  ROI for the C2 board is one
> year just on power saving.

It depends on how much load your server currently handle, and how your
cache is configured.

I'd start with looking at your server load. Arm still have lower
per-core performance compared to x86, so if you currently see high CPU
utilization by named, I'd stick with x86.

Next see how your memory cache is configured. That should be where
bind uses most memory. AFAIK by default max-cache-size is unlimited
and max-cache-ttl is set to several days. See how much memory bind
currently uses for cache, and then you can try configuring those two
parameters (e.g. set an explicit max-cache-size to 512MB) and see how
much memory bind (and the rest of the OS) uses then, and how well it
performs. If it's still acceptable, then you can probably go with the
1GB board.

Cache can reduce the number of queries issued upstream and is very
important on busy servers, but if you serve a relatively low number of
queries from your clients then you won't see much difference between
(e.g.) 512MB and 1GB cache.

-- 
Fajar