David's Computer Stuff Journal

Since hosting is the major expense for DedaSys LLC, and obviously a critical part of much of what I do, getting the right one is very important.

Naturally, "the right one" for me may not be the right one for everyone. I am a fair sysadmin for small numbers of machines, so I don't mind doing that myself - I don't need, nor want to pay for hand holding.

I recently moved everything over to Slicehost on the recommendations of friends, and am so far fairly happy with the experience. It's cheaper, simpler, and more flexible than Layered Tech was. To boot, I also like the fact that Slicehost is run out of St. Louis, Missouri, rather than some really expensive tech center like San Francisco or Boston. Hosting is basically a commodity, and much like you wouldn't want to put a factory in San Francisco, you don't want your hosting their either.

However, I discovered something annoying about Slicehost: they use x86_64 servers, which, per se, doesn't really matter to me - I use open source code that can run on any number of architectures. The problem is that this particular architecture uses more memory than plain old x86. Significantly more. My Layered Tech server with 1 gig of memory was hitting the swap space a bit, but the same code on a slice was swapping quite heavily, despite the fact that I'd moved PostgreSQL off to its own slice. Since I pretty much exclusively run Rails, I decided to look into Phusion's "Ruby Enterprise Edition", which is basically just some nice hacking on Ruby's garbage collection mechanism. What they've done is nice, and I may end up using it, but ultimately it's buying me space that I would also gain from simply moving back to x86. With that in mind, I decided to take another look at what appears to be emerging as one of Slicehost's main competitors, Linode, who do use x86 servers. Here are my results, which are admittedly not all that scientific, but what the heck - you're getting them for free, and they were pretty quick to whip up.

Service, Support, Setup

But before we begin with the numbers, I want to add a few words of caution. One of the big things about hosting, to me at least, is how they deal with unexpected random negative events. Connections going down, disk breakage, DoS attacks, and so on. It's really hard to get an idea of just what sort of people you're dealing with until you've "ridden the river together". I don't really know what sort of response times, uptime, and all that either Slicehost or Linode have, so there are potentially some big intangibles there that are not quite as easy to draw pretty charts for.

In terms of the console/setup/management tools, I liked Slicehost's simplicity more - Linode gives you more options, but they're a bit fiddly and cluttered feeling at times. For instance, Linode lets you pick how much swap space to give your disk image, but doesn't include a bit of javascript to balance out the swap and regular partitions, so that if you type in a larger swap number, you have to do the math and subtract that from the other number. Annoying, but not a big deal. Linode lets you pick various data centers in the US (no Europe, yet). Slicehost gives you the option to do backups of your disk images, which is nice, and something that Linode lacks.

Comparing plans

Since I'm interested in comparing hardware and machines I actually have access to, here are the plans I am currently signed up with, and the salient numbers:

<tr><th></th><th>Slicehost 1024</th>    <th>Slicehost 512</th>  <th>Linode 720</th></tr>
<tr><th>Memory</th> <td>1024</td>   <td>512</td>    <td>720</td></tr>
<tr><th>Bandwidth</th>  <td>400</td>    <td>200</td>    <td>400</td></tr>
<tr><th>Disk</th>   <td>40</td> <td>20</td> <td>24</td></tr>
<tr><th>Cost</th>   <td>70</td> <td>38</td> <td>39.95</td></tr>

Memory / Dollar:

Bandwidth / Dollar:

Disk / Dollar:

Linode mostly comes out ahead, but not by that much, except for bandwidth. However, let's take a crude look at x86_64 vs x86 memory usage.

First, ./script/console (a Rails console) for the same code base on two different machines, showing the virtual memory size (VSZ) and resident set size (RSS):

And just to look at something else that's a bit smaller, I ran the following script:

puts File.open("/proc/self/status", "r").read

And got the following data:

Being charitable with those numbers, we get x86 taking up 77% the memory that x86_64 does. So let's add that to our comparison of how much memory you're getting per dollar on Slicehost and Linode:

Wow! That's a fairly significant difference.

Performance

That's most of what we can glean from published numbers, and running a few simple experiments. However, there's another factor that's important: performance. "Virtual Private Server" systems, or simply VPS's, got a bad name in the past because they were "overbooked" - too many virtual servers competing for the same CPU resources on one machine. Slicehost and Linode both look like they want to avoid that kind of bad reputation, and so far all the systems I have used have felt snappy and responsive. Now here's where we get really unscientific... I decided to try and do something, even if it wasn't much, to get some kind of objective measurement of what kind of CPU I was getting on the machines. This is really unscientific, because the machines do have other duties (I don't have the cash, time or inclination to set up random servers just for testing), and of course, who knows what else is sharing the computer with my systems: if you get a relatively unused computer, you can apparently pick up extra cycles for yourself, over and above your guaranteed minimum. But c'est la vie, and so I decided to do some numbers anyway. I picked a C implementation of mandelbrot from the language shootout more or less "for the hell of it" (I'm going to keep repeating "unscientific" and invite someone to do better tests than I have). I ran this code every 20 minutes for a couple days, and then averaged out the run times:

As expected, the higher power Slicehost 1024 machine wins out in terms of raw speed (less time is better), but not by that much over the Linode system. Indeed, when we factor in the relative prices, Linode comes out ahead, again:

So it looks like we're not paying a CPU penalty for having more memory, bandwidth, disk, etc...

Notes

• Nothing in these statistics is indicative of future directions that both Linode and Slicehost might take. Slicehost was recently acquired by Rackspace, and that could have effects on the service they provide. Maybe one or both will come under financial pressure and start "overbooking" their servers.
• The spreadsheet I used is available via Google docs, for the curious. I did most of the work in OpenOffice, and then uploaded it though, because working with the web spreadsheet was kind of painful. Unfortunately, you can't select non-contiguous data ranges in the Google spreadsheet, so the labels are interspersed with the data. Yuck. Also, Google docs doesn't handle 'time' values nicely, which is what the performance data was originally. The spreadsheet is here: http://spreadsheets.google.com/pub?key=pVDeZF6ire2YwATBYb4mBKQ
• The standard deviation on the processing times is higher for both slices than the linode system. Not quite sure what that means in terms of what's going on under the hood, but I thought it was interesting.