Sometimes you get an idea, Canadian Tire has a sale and tada you have a brand new Roomba to play with.  In this case a Roomba 530.  The Roomba has been very well documented and there are plenty of reviews out there so I’m not going to do that here.

With a 16 month old & a cat running around the house, there is little time to clean most days and it doesn’t take long till the main floor gets full of crumbs, Cheerios and  assorted pet bits.  It’s still early days but our Roomba has been able to clean up very well after our little monsters and with significantly less effort than pulling out the hose for the central Vacuum.  It’s even been profitable as it has some loose change in its dust bin this morning.

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In a moment of not doing what I should be doing I decided I needed a stand for my iPod Touch so I could watch some video I had recently loaded on it.  What to use?

As luck would have it I had an old LTO-4 case sitting on my desk destined for the recycle bin.  30 minutes later and most of the LTO case is in the recycle bin, I have an iPod Touch stand and I no longer have a spare moment to watch that video.

This is not exactly stellar work but it is fairly acceptable considering I was working with scissors and dull side cutters.  Not stellar but effective.

So after being on the phone for over an hour with Telus “tech support”, I finally discovered the default PIN2 for their SIM cards. Not that tech support was any help. The first guy I talked to only had one thing to say to me:

We don’t have it, so it doesn’t exist.

Despite my best efforts, I could not convince him to ask anyone else at Telus, or even admit to me that there was such a thing as a PIN2. After a while he asked me if I would like to try to explain the issue to someone else (which is phone-support-guy for “I’m tired of dealing with you, can I please hand you off to someone else?”) and I said sure, go ahead. Pretty much the same deal with the second guy, but at least he didn’t hang up on me. I almost got the second guy to say that there was a PIN2 but that they didn’t know what it was, but his mantra ended up being “It’s not in the system, so it doesn’t exist.” I asked him if he knew anything that wasn’t “in the system”, at which point he became very quiet. He refused to, or couldn’t, tell me what the weather was like today, so I guess there’s no weather widget in their system… He also had no idea what color his socks were.

Finally, I guess his shift was up, so he asked me if I would like to speak to a third tech support representative, and I said “sure, follow your phone-support-guy training manual and pawn me off on someone else”. I don’t think he said goodbye, but at least he didn’t hang up on me. The third guy I got started off down the same tracks, but I confused him by asking some unrelated hypothetical questions, then BAM! – before he knew it he had admitted that PIN2 codes had existed for years, and it was likely that all SIM cards had them, even though the carrier might not use them. He also confirmed that they were not anywhere “in the system”. I then asked him how things got into “the system” and he said that he couldn’t answer that. I think the people who put stuff “in the system” should stuff themselves “in the system” – if you know what I mean…

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I still don’t understand exactly why OS X ships with Delayed ACK but it sure does kill network performance immensely – at least with a Freenas based server.  Modifying the Delayed ACK parameter will greatly improve you OS X network performance.

Today I was transferring a few files from the server to a Macbook running Leopard 10.6.2 and found it pokey.  A quick check of the network throughput revealed ~275KB/sec over a wireless N connection.  A quick look at the delayed ack reveled a value of “3″.  I changed the value of “3″ to “0″ and throughput jumped to 4+MB/Sec.  Much better.

To check Delayed ACK Value
$ sudo sysctl -a | grep net.inet.tcp.delayed_ack
kern.exec: unknown type returned
net.inet.tcp.delayed_ack: 3
To change Delayed ACK Value
$ sudo sysctl -w net.inet.tcp.delayed_ack=0
net.inet.tcp.delayed_ack: 3 -> 0
A good read detailing this phenomenon

TCP Performance problems caused by interaction between Nagle’s Algorithm and Delayed ACK-Stuart Cheshire

Update:

When I posted this I forgot that “sysctl -w” does not survive a reboot, it simply makes the setting active immediately.  You must create /etc/sysctl.conf with net.inet.tcp.delayed_ack=0 in it for the setting to remain persistent.  Personally I do sudo -s, add password and use vi to create the sysctl.conf file.