Dual vs single CPU machines

[Barry Sollitt]

Hello all,

I am after a bit of advice as I am currently architecting a new HP-UX server solution.

I am proposing a minimum of 2-way machines for the entry-level servers (rp34,rx26).

I am just concerned that management will ask me why go for 2 when 1 will have enough processing power(TPMs)

My arguments so far are:
Redundancy - assuming they are single core
Performance - for future applications
and that dual core CPUs are opn the scene anyway.

Does anyone have any other practical ideas as to why dual CPUs are better than 1 ?

[Mic V. · Accepted solution]

Actually, sorry to say it, I can think of an argument against (I was really trying to think of arguments for, honest!): if you're doing any licensing that's CPU-based (such as Oracle, last time we discussed), having more CPUs sooner is going to penalize you in terms of licensing $$$.

I guess one kind-of argument "for" is that if one machine's load outstrips the other, assuming the CPUs are compatible, you could take a CPU from the less-loaded machine and put it in the more-loaded one, giving you a stop-gap measure while management decides to buy something.

I'm with you, but this is what I got shot down on last time out.

HTH,
Mic

[Ravi_8]

Hi

I agree with your arguments, but you have to think of licensing cost at the same time.

No doubt 2 way machines speed up the process, we use 2 way machines for build purposes, for dev and testing it's 1 way machines

[A. Clay Stephenson]

This all comes down to the performance data for your applications. If you are CPU bound then it makes sense to buy more processors but if you really want to feel dumb, try yo explain to your boss why your brand new 2 CPU box (which you expected to be nearly twice as fast) is only 1.05x as fast because you applications were i/o bound. If you are spending limited amounts of menory, it is important to identify where the largest improvements can be made. By not means am I saying that more CPU's is not a good thing but that you may get greater marginal utility from spending it on improved i/o (more i/o channels) or memory. If you are doing CPU-intensive task (e.g. Finite Element Analysis) the more CPU's make a lot of sense. You really have to get some metrices (e.g. Glance) for your existing applications and then you will know how to best spend your money.

[Barry Sollitt]

thanks guys....

[Rory R Hammond]

Everybody is right. Extra licenses and I/O bound can be a problem. So can memory.

When it comes to new development, Platform Sizing is really an art. If you are moving an existing applications or upgrading you can guess better. I am in favor ar extra CPU's. A looper can take a whole CPU. A single processor bound by a runaway process is hard to break in to and kill. Trouble shoot is also harder.. My experience is A right sized box with good memory, good I/O distribution and dual processors is better suited for handling PEAK processing of busy applications than a Single processor. Number of users, type of Jobs also affects the choice. The more users and more running processes would also play in to the soup.

Rory

[Dave Wherry]

Another angle I always like to look at is how many CPUs can go in a server. I don't like to max out a server on day one, unless I'm very sure that environment or the load on the server will not grow.
If you only need a single CPU, of course the entry level HP servers can handle two. You can start with one and add a second later if needed. If that application needs two now, I'd go with a server that can acoomodate four. Always leave some headroom for expansion. It's usually easier to extra CPUs approved than a box swap.
Then there's another option. The next generation processors will provide better performance so swapping out CPUs when faster ones are available is also an option. HP has historically given a generous trade-in allowance on CPUs.
Then there is also chasis considerations. How many I/O or memory slots do you need?
So as you see, the real answer, as usual, comes down to it depends.

[Florian Heigl (new acc)]

Licensing is a big issue, but I think the added potential workload should already be worth that. Also You gain a very beneficial behaviour under very high load, which at least for me is the bigger argument.

I'd try to get a system with one dual-core cpu installed and a socket for a second one.