Tis the Season… for Buying my Dynamips PC

Tis the Christmas season, and among other things, it’s time to shop. I’m ready to get out the checkbook and buy a PC to run Dynamips, with enough umpfh to never ever worry about whether it’ll run 12 routers or so concurrently. Well, maybe that’s a bit naive, but in today’s post, I’ll tell you about my research, suggest two sets of specs for buying a DM PC, and ask the rest of you shoppers to help me find a good place to buy it.

If I had a lawyer, I’m sure they’d tell me to disclaim all this as well, so… everything here is based on what I’ve read, and not what I’ve seen, so be careful. I will let you know how it goes once I’ve bought and tried it out.

First, let me tell you my process to get here. I read over posts to this blog space, and many posts in Hacki’s forum (7200emu.hacki.at). Hacki has several forums related to Dynamips, and one specifically focused on the choice of PC hardware and OS to run. I looked for posts where someone wrote things like “I can run X virtual routers (VRs) on such and so hardware and software”, and collected the data. It some extra time to collect it, but I figured some of you might like to see it collected. I also listed any random thoughts I had read regarding overall performance or hardware issues – things to think about when ordering. You can see that working document here. If you review this doc, you can click the links from which I found the info, and  quickly see the background.

(Side note – the PDF’s links don’t work. You can copy/paste from the PDF into the URL field. Sorry, I spent an hour on getting the Word-to-PDF conversion on my new MAC to work and not mess up the URL – if anyone knows the trick to keeping the URL in tact, lemme know…)

Next, here’s a list of requirements that I developed along the way. I wrote something about all these during the last 2 posts:

• Run 12 VR instances concurrently, with them doing things that are reasonable for DM VR to do.
• Connect externally via Ethernet to real switches, with at least one such connection using 802.1Q.
• Run the most recent IOS versions (I’m counting that as 12.4T for now)
• I’d love a rack mounted server, but it may be too much more $ versus a deal on a comparable desktop.

Here are some of the conclusions I came to after reading the various posts:

CPU: Almost all the posts I saw that suggested it could meet these requirements listed a processor with 4 cores. A little research lists Intel’s “Core 2 Quad” which is a series of Intel processors with 4 cores. (link to Intel for this CPU). Comparables include the AMD Athlon II X4 (X4 = 4 cores), or the many Xeon Intel processors. The I7-920 CPU I was originally looking at has 4 cores, plus hyperthreading, for 8 concurrent threads.

RAM: Most listed 4Gig as what’s working well at the dozen or so router level, which shouldn’t be too expensive at today’s prices. However, many comments referenced how it is helpful to choose an IOS feature set/version so that the memory required is smaller, resulting in better performance. One of my main objectives is to use this DM machine to model things more quickly than re-cabling my gear, but the things I model will typically need to be the more recent (and more memory intensive) IOS versions. So, I’m considering whether I should look for 6 or 8Gig to start, or even buy a system expandable to 16 Gig, just in case.

Ethernet: After the many suggestions for USB Ethernet cards, I think I could get by with a system with 1 built-in 10/100/1000 NIC, and one PCI slot, and 4 USB ports. In reality, I think I’d have at most 4 connections to external switches in a typical topo anyway, and only one of those as 802.1Q, so I’m planning to use USB Ethernet plus 1 PCI card so I can have some flexibility in what Ethernet card I use.

A couple of other items popped up as considerations for what hardware to buy. First off, many folks suggested that the more the routers do, that the system may slow down. So, throwing a little more $ at the CPU may make sense. However, I drew the conclusion that other factors may matter more – items as varied as using an older IOS (less mem), starting IOS images in a particular sequence, and changing IdlePC value if you see it’s not working well any more. Short version here: throwing hardware at it as a strategy to avoid the extra time to look at such issues may not be enough; you may have to still be watchful for such things. Also, an off-hand interesting comment was to make sure the CPU cooling worked well, so the CPU didn’t slow down once it warms up.

More next page…

A few things that could have mattered that didn’t seem to:

1)    Disk space and speed. No one much discussed needing a faster disk, or using solid state disks (SSD), other than a few comments here and there. Lots of people claimed good DM performance without even mentioning any disk requirements. It’s tempting to get a small SSD just in case…

2)    CPU speed – while some folks mentioned the speed of the CPU, most just mentioned the CPU type, almost all of which had 4 cores, and some of which had hyperthreading to boot. No other facts to quote here, but I’m thinking that a CPU with more concurrent processing is the bigger issue than the speed.

3)    No one much discussed speed of the RAM, or DDR2/DDR3.

So, the next step is to choose a set of specifications, and then I’ll go shopping (hoorah!). From what I can gather reading everything, I think a minimum requirement for my DM server with a high confidence that it would work for my requirements would be:

• CPU with 4 cores (Core 2 Quad, AMD Athlon II X4, various I7 and Xeon), no hyperthreading required
• 4Gig RAM , expandable to 8G
• HDD – to suit
• 1 built in plus 1 PCI slot, or 2 PCI slots
• At least 1 USB Ethernet and 1 PCI Ethernet card to start testing

I personally would bump it up a little, and say:

• CPU with 4 cores plus Hyperthreading (I7-920? Xeon?)
• 6G DDR3 RAM to start
• Expandable to either 8G or 12G (price differences will impact the choice here)
• Same HDD, Ethernet as previous list

So, there’s the nice theoretical spec list. I spent a quick few minutes shopping at dell.com, and found a Dell Poweredge T110 (starting where Vito was suggesting last week), for $429 list, with a need for more RAM (comes with 2Gig), which would be cheaper to buy elsewhere I’m sure. The CPU is a Xeon X3430, which has 4 cores but no hyperthreading. So, with a little more memory, it would meet the first of the two specs.

I plan to shop for this thing before I blog again – in 2010. I’ll pop into the blog for replies between now and then, but I’m trying to mostly be off the last 2 weeks of the year. If you see a good place for a deal in these spec ranges, feel free to post the site (but please disclose if you have a relationship with the seller). Thanks for all your help on this project, folks – I feel like it’s been Christmas already with all the help you folks have been giving me. Merry Christmas, or happy whatever holiday you may be celebrating, and I’ll blog with you next year!

Wendell