Alex Hopmann’s Blog

Building a silent PC- you failed!

On Friday I finally got all the bits together for me new home RAID array. This one is a Sans Digital TR4M 4-space ESATA enclosure plus 4 Western Digital GP 1TB drives. Building it as Raid5 it looks like the total capacity will be 2.8TB (as the computer measures it, not as the drive companies market it).

I started it formatting, skipping the “quick format” option. That was over 24 hours ago and its at 36% right now. Which points out one of the biggest problems with large drive arrays (or any kind of large storage)- if you aren’t careful managing it can be a total mess. This does make me a bit happy that I decided to go with just the 4-drive array rather than holding out for a full 8- the bigger one would be even more of a mess to manage at times.

For my media-PC I purchased a silent video card. Gigabyte makes the SilentPipe series for several of the Nvidia models and it seemed like a good idea to be able to get a card with decent graphical power (not top, but at the time it was better than any of the other cards I had) and no noise.

The catch is that when building a Media PC you need to keep in mind the overall system. The SilentPipe GF8600GTS has two problems- first of all its form factor is kind of big- the cooling fins stick about a half inch over the normal height of a PCI-express card. In a full sized case this would be fine but in the Zalman media-case I have there is only the exact room for full height cards and the extra half inch means the top of the case doesn’t really fit right.

The second issue is heat. The card runs correctly, but overall it does run pretty hot and since its not blowing the hot air outside the case itself it places extra heat load on the rest of the system + relies on the existing case fans to create air moment through its fins and out its vent. I suspect this results in my overall case fans running higher more of the time, so in the end I fear that I’m actually running a more noisy system for trying to use a silent video card. Instead of adding one relatively slow running video card fan I’m pushing the main fans faster and higher RPMs create a lot more noise.

Cool site with focus on Seattle music happenings….

Back in March Dare Obasanjo said he was going to stop blogging. Luckily it seems like he didn’t carry through his threat very well and has had a ton of great posts recently.

Dare posted on functional programming, Map/Reduce/Filter in C# 3.0 including some nice background on the topic. I’ve been getting into Python lately which has some really elegant support for anonymous functions, list/collection operations, and specifically things like map/reduce/filter. This is also an interesting approach on some similar techniques in PHP.

Dare also did an interesting post on techniques to dark launch / gradually ramp up new features. The idea is that you want to try out a new feature without risking taking down your entire user base at once.

Some other really simple approaches include putting a hidden iframe into existing pages that access the new feature. Its a really easy way to isolate it from the rest of what is going on for your site. One thing to keep in mind is that as you dark-launch a feature its really important to figure out how you can throttle it up/down. If you have 20 front end servers, maybe you can deploy it only on a certain set of them or else your pages can only serve it up a certain random percentage of the time. This way you can start it up on a very low load (say 1% of the requests) and slowly increase it to try it out more. If you start having some performance problems in your data center, just kick it down a couple of notches.

Deploying to only certain specific servers can be especially interesting because it can (if done right) focus the load on those servers. So those servers behave the way the whole system will once the system gets fully turned on, but don’t have the same risk of taking your whole environment down.

Yesterday I wrote about problems installing Vista SP1 on this machine. Running the “download and run it yourself” installer worked fine with one little glitch. The issue was that I first downloaded the SP1 setup that only contained 5 languages, thinking “hey, I only really actually care about English”. The catch is that it won’t run if you have any languages other than those 5 installed. I had previously installed a ton of languages since they were just check boxes in Windows Update.

Uninstalling languages turned out to be a nightmare. First of all, you can’t uninstall from “Programs and Features”, you have to go into “Regional and Language Options”, go into the “Keyboards and Languages” tab, click a button, click another button. Then most of my attempts to remove languages would fail (after sitting doing something to my computer for what seemed like 30 minutes), PLUS it requires a reboot after each one (even though I’m uninstalling languages I’ve never ever used).

So the solution ended up being downloading the “all languages” version of the Vista SP1 package. The 20 minutes the download took was way faster than uninstalling the languages. Upgrade felt like it took a long time- I could be wrong but it feels slower than initial setup (which does make some sense since initial setup can just write an image down on your disk while upgrade is presumably doing more real work).

All is well now and so far the machine is running smoothly.

Brad Feld posts about Office hours during college and how he tries to do similar things now at their TechStars incubator. We have a different take on office hours at DeepRockDrive but so far it works out really well and I thought it would be interesting to share.

When I started working with DeepRockDrive the technology folks up here in the Seattle area didn’t have a real office at all yet. Folks just met most days in a coffee shop and would hang out and work on the code. There were a few contractors scattered off around various parts of the world and people would often work at home. Everyone would log in to Skype all day in a common chat room so you get the similar concept to shouting over to the guy at the desk near you.

We have had an office now for several months, but its over in Bellevue. Our staff is all over the Puget Sound area and traffic isn’t so wonderful around here most of the time. I was hoping we could maintain some of the culture of being able to avoid wasting 40-60 minutes a day in traffic plus the advantages of being able to concentrate at my home office (not to mention reducing the environmental impact of all that driving especially in stop and go traffic). At the same time to act as a well oiled agile startup we need to have great communication with each other and it was sometimes really difficult to find a time when all the right people were around to discuss a given topic.

What we came up with was the concept of “core office hours”. This is roughly Monday, Wednesday and Friday from 10am to 3pm. During those times people are expected to be in the office (with the obvious exceptions for vacation, travel, important appointments, etc). Those are great times to schedule a meeting, plus you can usually pull together the right people for an impromptu meeting for just about anything. But, with the limited hours this also helps prevent our schedules from filling up with constant meetings so we have solid times to get code done, tested, write important documents, etc. On Tuesday and Thursdays I can avoid getting in the car at all. On Monday, Wednesday and Friday when I do need to go into the office I can do it at a time when traffic is WAY better (20min vs 40-60) plus its a nicer time if you want to bike too.

So far overall I’d say this system is working great, but I do have a few thoughts about some considerations that are necessary to make it work-

• It is not going to work for all job roles. Some types of jobs require you to be at the central place where people can be there together. And the job needs to be something where the output is pretty measurable- if you can’t tell if someone is goofing off, its going to breed ill-will. If the job is something where the results speak for themselves (amount of code written, bugs found, etc) it is a good fit.
• It is not going to work for all people. To make this work you need people that are very self-motivated and self-starting.
• The Skype thing helps us a ton (although any other form of live chat-room with presence information also works). It helps both give us that ability to communicate and get problems solved with colleagues in real time, as well as helps people be visibly “on the job”.
• It helps to have good network resources. We rely on a combination of the Skype stuff, as well as GMail, Google Docs, Basecamp, and an SVN and Trac server that we have deployed in our data-center. I’d also point out that all of those services are accessible without VPN so our staff can easily work on stuff from home / a cafe / vacation / the road. In theory having to VPN shouldn’t matter but I’ve always found it to be a big barrier to getting real work done.

I’m having a problem installing Vista SP1 on my main workstation. Microsoft Update keeps throwing a Code 80070570 error which has no real description. The best hint I can find searching the net is that it might be related to some disk issues, but running a CHKDSK to fix errors didn’t make the problem go away.

My next attempt is to download the standalone upgrade- its possible the problem I’m experiencing is with Microsoft Update rather than the service pack itself.

My buddy Eric Berman writes about how badly the major airlines have screwed up their recent pricing changes where they charge for checked bags and nickel and dime you on every bit. For what its worth Eric is a former exec at Expedia which I think qualifies him as an expert on aspects of the travel industry. The main point is that there were totally different ways to position this- “we aren’t going to charge you for stuff you might not use”. They sort of successfully did that with most of the changes in in-flight meals. Considering how bad they were I haven’t minded that they don’t provide them anymore as long as I can bring my own food on. What scares me about the checked baggage thing is that the result will be even more people competing for the limited overhead space, and many of them will be infrequent travelers with huge over-packed bags. This could easily turn into a mess with 15 minutes of extra boarding time which would quickly cost the airlines more than they are saving in the first place.

Meanwhile Signal vs. Noise writes about how Alaska Airlines did some smart research to redesign the check in area in Seattle with a projected savings of $8 million this year. Alaska has actually been doing this kind of thing for years- a very long time ago they were one of the first to put kiosks in the Seattle airport. Back then I was flying them a lot and it was great to walk from the parking garage and be able to hit the kiosk right away (before you got up to the full mess of the check-in area) and it would print out your boarding pass with the gate # right there. No milling around looking for the right place and the frequent Alaska travelers got to skip the whole mess.

Its things like this (as well as my recent experiences flying from Washington DC back to Seattle) that put Alaska Airlines in the “new airline” camp. They may have been around for 80 years or so but mostly they still behave more like Southwest and JetBlue than like an old-school airline (American, United, etc…)

Dealing with cache expiration with memcache has some subtle gotchas that many people ignore at first. Lets say you are using memcache to cache an object that you want to refresh at least every 5 minutes. The typical pattern for this would be (in PHP)-

$myobj = $memcache->get('key');
if($myobj == NULL)
{
  $myobj = LoadMyObjFromMySql();
  $memcache->set('key', $myobj, 300);
}

With this code you should expect to see one query on your database every 5 minutes. But implement this on a high capacity web site and you will probably see your MySql database get pegged every 5 minutes with a spike of a ton of queries. What is going on?

Notice that there is a time window in between the memcache get, the database query and the memcache set. This window isn’t large, but it could easily be 10ms. On a web site that is running 1000 requests per second you could easily have 10 different requests where the memcache get fails (because the object is expired), and they each hit the database before they update the memcache and everything is back to normal.

The solution is to not rely on memcache to manage the expiration. We can rewrite the code above to look more like-

$myobj = $memcache->get('key');
if($myobj == NULL || $myobj->expire + rand(0,120) < time())
{
  $myobj = LoadMyObjFromMySql();
  $myobj->expire = time() + 300;
  $memcache->set('key', $myobj, 600);
}

This way memcache still has an expiration for the objects, but its longer than our real target. For the first 300 seconds the objects always just get loaded from the memcache server. Starting at 300 seconds there is a tiny chance that each request will refresh from the database and update the memcache. This way if there is a large load on the server, the chances are that only 1 or 2 updates will happen, but that it will happen right away. If there is a lighter load within 7 minutes the object will eventually get expired for sure. So the chance that any given request will refresh the cache ends up being inversely proportional to the current load.

The above code of course relies on you storing PHP “objects” in the memcache so it can tag the extra expire property on. If you aren’t storing something that is already an object you can always create a new object that stores your real thing in a property called “data” and still uses expire. You will pay a small overhead for the object marshaling but it shouldn’t be too painful.