Broken PMTUD on Amazon EC2
While at Amazon re:invent I had the opportunity to complain to some Amazonians again about an EC2 bug which has been annoying me for a long time: The default firewall rulset is broken. I discovered this three years ago while debugging odd problems experienced by a Tarsnap user — sending a small amount of traffic worked fine, but as soon as large amounts of traffic started moving around, the TCP co
Software development final exam answers: Part 1
These are the answers, along with some commentary, for part 1 (Algorithms and Data Structures) of my software development final exam. Each question was graded out of 5, with points awarded for different parts of each question as described below; in some cases I awarded partial marks (e.g., 2 of 3 possible marks for part of a question) when someone had the right general idea but missed some details
Software development final exam: Part 1
This is part 1 of my software development final exam. If you haven't read that introductory blog post, please go read it now. Algorithms and Data Structures Is O(2^n) equal to O(3^n)? Why? What is the expected run-time of quicksort? What is the worst-case run-time? What is the difference between a binary tree [EDIT: that should be binary search tree] and a B-tree? When and why does this difference
Why Tarsnap doesn't use Glacier
Two weeks ago, Amazon announced its new Glacier storage service, providing "archival" storage for as little as $0.01 per GB per month. Since I run an online backup service, this is naturally of interest to me, and in the day following Amazon's announcement I had about two dozen tweets and emails asking me if Tarsnap would be using Glacier. The answer? No. Not yet. But maybe some day in the future
Why Tarsnap won't use DynamoDB
When I heard last Wednesday that Amazon was launching DynamoDB I was immediately excited. The "hard" server-side work for my Tarsnap online backup service consists mostly of two really big key-value maps, and I've spent most of the past two years trying to make those faster and more scalable. Having a key-value datastore service would make my life much simpler, I thought. Unfortunately, upon readi
FreeBSD now on all EC2 instance types
Six months ago I announced here that I had managed to get FreeBSD running on 64-bit Amazon EC2 instances by defenestrating Windows AMIs. That took the set of EC2 instance types FreeBSD could run on from three (t1.micro and c[cg]1.4xlarge) up to nine by adding all of the large and extra-large instance types; but FreeBSD still couldn't boot on "high-CPU medium" instances or on the "standard small" i
Automatically populating .ssh/known_hosts
One of the more irritating things about working with virtual machines is SSH host keys. Launch a new virtual machine. Get a new host key generated. Try to SSH in. Get a pesky warning message telling you that the authenticity of the host can't be established. Find the host key fingerprint in the virtual machine's console logs. Eyeball the two 32-character hexadecimal strings. Type "yes" and hope th
POSIX close(2) is broken
In the world of POSIX, everything is a file. Well, sort of. There's sockets and pipes, which behave rather like files except that you can't seek on them and they have some extra metadata. And there's devices, where sometimes you can only read and write appropriately-sized blocks, not individual bytes. And then there's terminals, which are all sorts of weird. But in all these cases, you've got a fi
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Software development final exam answers: Part 3
Supporting those who support us
Software development final exam: Part 4
Software development final exam: Part 3
Software development final exam: Part 2
Protecting sshd using spiped
Tarsnap now takes credit cards (without Paypal)
I will not be acquihired
Tarsnap outage
Speeding up Portsnap via geolocation
Playing chicken with cat.jpg
'Tis the season for giving