May 26, 2009

It’s the little things: Why 4Gbit fiber channel = 400MB/sec

Filed under: It's the little things — dalvenjah @ 1:04 am

Current Mood:Accomplished emoticon Accomplished & Geeky emoticon Geeky

I’m trying different things nowadays to see if I can’t be informative *and* fun! Well, at least informative. And maybe blog more regularly, too.

We’ll start it off with something that had been bugging me for a couple of years, for which I just found the explanation.

Computer work engenders some bizarre practices and tenets, but typically one could always rely upon the math. Since computer science departments grew out of math departments at universities, there usually isn’t a lot of wiggle room when it comes to the numbers — except for when hard drive manufacturers let their marketing departments call a 645GB hard drive a ‘750GB hard drive’. But other than the boil-brained, you could pretty much count on the fact that there are 8 bits in a byte, and that a 1 gigabit network connection would (theoretically) let you pass 1024 / 8 = 128 megabytes per second. The numbers were never perfect metric matches (like 1 meter = 100 centimeters), but they were consistent.

So it surprised me to find everyone who talked about fiber channel connection speeds saying that a 4 gigabit fiber channel connection can push 400 megabytes of data, a 2 gigabit connection 200 megabytes of data, and so on. “They must be taking a shortcut,” I thought, and didn’t give it much thought beyond some wondering as to why 4 gigabit fiber channel doesn’t pass the same amount of data that, say, theoretical 4 gigabit ethernet would.

It turns out I was partially dread-bolted clack-dish wrong, though, and discovered recently that there’s a good reason why fiber channel went metric. It’s still not as exact as I’d like, but the approximations were a bit more accurate than I’d thought.

Fiber channel uses an electrical encoding called 8b/10b encoding to carry data on the fiber (and copper, when used). It maps 8-bit symbols to 10-bit symbols in such a way that there won’t be too many 1s or too many 0s sent down the wire — they’ll roughly balance out. And much to my surprise, it’s not just because the designer had OCD and needed to make things come out even — depending on how the signal is carried, if there are too many 1s in a row, capacitors in the circuit that might be used for filtering and such can get charged up to a point that they’d interfere with the signal. So 8b/10b encoding means that for most of the 8-bit values (think ASCII table), there are two ways to encode each character. So, for example, when you send an ‘A’ down the wire, you can choose an encoding with more 1s or more 0s to make the bits balance out.

8b/10b encoding also provides for some extra slots for control codes like the arbitrated-loop loop initialization code and such, so that you don’t have to worry about escaping real data in case your control sequence shows up in a live data transfer.

What this means is that for every 8-bit byte you send down the fiber, it gets converted into a 10-bit byte, and 10 bits get sent for every 8 bits of real data you mean to send:

So when you do the math, instead of 1 gigabit fiber channel being 1024 / 8, it’s actually 1024 / 10 = 102 megabytes/sec, roughly. The line rates aren’t quite exactly on the gigabit mark, but the math is close enough to estimate. Remember that the gigabit/sec unit refers to the line rate — how many bits can go across the fiber in one second — and megabytes/sec refers to the amount of real data (8-bit data coming from or going to a disk) that can be passed in one second. So:

  • 1 gigabit fiber = 1088 megabits/sec on the line = 108.8 megabytes/sec of real data (not 128 MB/sec)
  • 2 gigabit fiber = 2176 megabits/sec on the line = 217.6 megabytes/sec of real data (not 256 MB/sec)
  • 4 gigabit fiber = 4352 megabits/sec on the line = 435.2 megabytes/sec of real data (not 512 MB/sec)
  • 8 gigabit fiber = 8704 megabits/sec on the line = 870.4 megabytes/sec of real data (not 1024 MB/sec)

(Per a reminder from MC: these are the theoretical top-end speeds you’ll see, and not what you’ll see in the real world. At least with ethernet, if you get 80% of the theoretical limit, you’re having a good day. Thanks!)

I hope this was at least a little useful, and perhaps even thought provoking. Okay, maybe not. But it’s a nugget of possibly useful information that I discovered recently, and thought I’d try to pass along.

References:

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April 5, 2009

Post 300! Link dump.

Filed under: Just life, linkdump — dalvenjah @ 11:37 pm

Current Mood:Rushed emoticon Rushed & Working emoticon Working

Running around a lot. Not in a bad way.

Things I’ve found, with some musings:

Some more links and a bit of opinion now. Watch out!

Some business-ey things. Is your organization designed for humans? can spur off an interesting thought experiment about how businesses should be structured. The traditional model chooses people and puts them in slots. Person A designs the widget, person B makes the widget, person C markets the widget, and person D sells the widget. I think that companies where all people from A to D can interact and share duties — Person A and B can talk to person C about how to market, and person D can relay customer information and suggestions back to persons A and B. Companies where people are too siloed have problems — designers design products and never really find out about how their customers really use their products, or what problems they have. There are a bunch of companies I’m familiar with that are blurring the lines between divisions, and letting engineers and designers *gasp* talk to customers. I think this is a good thing. (Link via Kottke.org)

Five questions every mentor must ask. I think it applies (as the author states) equally well to anyone (especially internal folks!) who are looking at a business or a process within an organization, as well. At the very least it gives you a framework to start from when trying to “think outside the box”. (Egh. I need to work on my synonyms.) Via the New Shelton Wet/Dry.

This is something I’ve run into in the past. How does a technical person effectively convey to HR or a recruiter what they’re looking for when relying on them to screen resumes? Not sure if this comic will help.

In an interesting experiment, a UCLA psychologist showed that talking about bad feelings helps lessen their impact. So talking to one’s priest, therapist, psychologist, even your S.O. really does help one cope with overwhelming emotion. Possibly found via The New Shelton Wet/Dry.

And in other news, here are Ten things science says will make you happy. I try to follow at least a few of these. I don’t always do a good job.

And last, to make myself happy, I’ve been listening to The Birdsong Radio web site at work. Lovely recordings of just birds singing their tiny hearts out.

February 19, 2009

sick link dump

Filed under: linkdump — dalvenjah @ 11:13 pm

Current Mood:Silly emoticon Silly & Sick emoticon Sick

I think I did one of these before. I’ve gotten the flu now twice in less than six months — certainly not a happy thing. I appear to be past the I-need-a-body-transplant-this-one-is-broken stage and into the messy-remnants-don’t-cough-now-but-your-nose-is-running stage. Here’s hoping for a full coherent day tomorrow.

So in the last throes of fever-induced delerium, here are some links i’ve been saving up. Like the last one, unfortunately, I didn’t record where I got them from — so they’re probably from the usual suspects — Reddit, Digg, Neatorama, among others.

  • Not to seem like an amputation fetishist, but I think these two people have the right idea — if you have to have a replacement limb, design it to be sleeker and better than the one it replaces. This prosthetic arm by Hans Alexander Huseklepp, and this prosthetic leg by Jordan Diatlo (possibly both via NOTCOT). A prosthetic certainly shouldn’t look pedestrian. (oh my. I’m probably going to hell for that one.)
  • I knew that Naugahyde existed, but I had no idea that it came from real naugas. I think this one came from Kottke.
  • I just like this headline: Blowfish testicles poison seven. Again, probably going to hell.
  • I love the 50s-movie-poster-style “Humans are among us!” ad campaign for the Sci Fi channel.
  • Two important notices on a utility box. Didn’t I say I’m probably going to hell?
  • Here’s a scary idea that’s almost Hugo Drax or Max Zorin in its scale: Herman Sörgel, a German architect, wanted to build a dam across the Gibraltar Strait and drain the Mediterranean Sea. Called Atlantropa, ignoring the environmental impact, it was purported to provide space to relieve overpopulation, and large amounts of farmland (including irrigating the Sahara Desert). It’s almost British Empire in its audacity. The poor guy couldn’t get anyone — the pre-WWII Nazis or the post-WWII European countries — to support the plan, even though he shopped it around for 30 years. You can’t say Sörgel didn’t think big.
  • The Beatles, seen from the top down.
  • Eastern Bloc Lolcats, translated?
  • The Trilogy Meter. Not terribly inaccurate.
  • The mystery of Ireland’s worst driver, solved! Those wacky Polish!

And now, as possibly previously seen, but necessary for repeated viewing, Phill Jupitus does Eddie Izzard — remarkably well.

He also does a remarkable Stephen Fry:

February 7, 2009

codetwit

Filed under: Computer joy — dalvenjah @ 10:15 pm

Current Mood:Accomplished emoticon Accomplished & Geeky emoticon Geeky

I should also plug CodeTwit.com — it’s a site where some colleagues and I are starting to post tips and tricks we find when doing general computer work. My first post was one on how to diagnose fiber optic problems without going blind using a cellphone camera. I still want to put some useful computery things here, but with luck that site will become a good repository for random hints.

catchup linkdump

Filed under: linkdump — dalvenjah @ 10:11 pm

Current Mood:Giggly emoticon Giggly & Tired emoticon Tired

Been lagging in the posting thing lately. Here are some links I’ve saved up for a while; unfortunately I’ve forgotten where I found most of them. A good majority come from Digg or Reddit, but others come from other web sites.

More soon. But for tonight’s video: as you can see from the next few posts, we’ve recently discovered Bill Bailey — extraordinary musician, comedian, and overall smart guy (who attracts nutters). We recently got Bill Bailey’s standup DVDs and relished them; he’s great at standup, did a hilarious TV show for the BBC (that he posted on YouTube), and did a great collaboration with an Indian band for an encore. He’s also a regular on Never Mind the Buzzcocks and QI.

Anyway — enough gushing. Once they start in you’ll recognize the tune, done in a spectacularly different way.

January 7, 2009

Medium sized linkdump

Filed under: linkdump — dalvenjah @ 9:42 pm

Current Mood:Mellow emoticon Mellow & Tired emoticon Tired

This week I found things.

For the video, still on the Bill Bailey thing. This time he outlines what makes U2 great.

January 3, 2009

Shortish linkdump, and some comedy

Filed under: linkdump — dalvenjah @ 3:11 am

Current Mood:Amused emoticon Amused & Tired emoticon Tired

Shortish linkdump tonight, mainly because I wanted to post the video at the end.

We have:

OK — here’s the video. I’m a fan of Eddie Izzard and Dara O’Briain for smart stand-up comedy; tonight on Videosift, I find that they’ve been posting stand-up clips from Bill Bailey, who up till now I’ve only seen in clips from QI. (Go sign their petition to release the DVD in the US — want intelligent funnythings on TV please!). Play. Laugh. Enjoy.

Bill Bailey on “Acts of God” rental insurance clauses:

And Bill Bailey on Britain:

January 1, 2009

new year’s linkdump

Filed under: linkdump — dalvenjah @ 11:59 pm

Current Mood:Amused emoticon Amused & Relaxed emoticon Relaxed

Welcome to 2009! This year I resolve to do more things better. (In all the various and interesting ways that sentence can be parsed.)

Meanwhile, a bit of a backlog of links.

And now, a video made possible with inexpensive editing and compositing software, and a man or few with lots of time on their hands, that reminds me of reading USEnet TV-show crossover humor fiction stories fifteen years ago(!?): Star Trek meets Doctor Who: The Christmas Special. Thank you, Reddit and Mind Grapes.

December 17, 2008

link dump

Filed under: linkdump — dalvenjah @ 1:19 am

Current Mood:Accomplished emoticon Accomplished & Tired emoticon Tired

Tonight I made more apple galette things, and they were the best yet. I really need to blog the pie crust recipe and galette recipe. Soon.

For now:

And now, straight off of youtube, someone took the Quantum of Solace opening credits and pasted in Joe Cornish’s proposed theme song. I haven’t seen the movie yet, but I understand it’s much better this way.

December 14, 2008

link dump

Filed under: linkdump — dalvenjah @ 3:11 am

Current Mood:Awake emoticon Awake & Tired emoticon Tired

Today, I marveled at how well Network Appliance’s cluster failover feature worked. One head of a pair lost communication with its disks, the other head took over, and nobody noticed.

Links!

Tonight, via Reddit, Peter Sellers beats out William Shatner by about 40 years. A Hard Day’s Night in the style of Sir Laurence Olivier’s Richard the III.

December 11, 2008

link dump

Filed under: linkdump — dalvenjah @ 12:29 am

Current Mood:Exanimate emoticon Exanimate & Tired emoticon Tired

Today there was food. I’m getting better at the mini-apple-galette things. And I think I’ve found my pie crust recipe. I’m going to have to post both.

Links!

  • I think this site has made the rounds before, but it’s amusing if you’ve not seen it before. Let the thing load and wait for it. Via Reddit.
  • Lovely pictures of wintry snow and ice — I haven’t had to shovel it, so it’s still pretty. Via Reddit.
  • I’d go for this bailout — give everyone a sum they have to use to buy things instead of paying down debt or investing with. Like the “stimulus checks” but guaranteed to be shoveled back into the economy. Via Reddit.
  • This is rather moving; the surviving Tuskegee Airmen to be invited to Obama’s inauguration. And it’s Sen. Feinstein of California of all people who sent the invite — not someone I agree with a lot of the time, but she did an impressively good thing this time. Via Reddit.
  • Not normally a fan of Reader’s Digest, but every now and then they do an impressive article. Here are eighteen memos to President Obama from various political and cultural leaders. A few (esp. Grover Norquist’s) surprised me. Via Reddit.
  • In software — this guy’s comments about letting an operating system do what it’s good at (in other words, don’t think you know better than the OS does how to shuffle your program’s data between RAM and disk are at least something that should be taken into consideration when you design something intended to be fast and efficient. Via Reddit.
  • For the aspiring MacGyvers out there, or at least someone who always wants to be prepared, Parachute-cord bracelets. So you’ll always be ready to rappel down the side of a (two-story) building. Via NOTCOT.
  • Here’s a fun metafilter thread to read (especially in lean times!) — what pieces of everyday life can be upgraded, usually for not a lot of money, for something durable and well-made and even pleasurable to use. It drives me nuts when people will buy a poorly-made knockoff or off-brand item because it’ll save them a few bucks, then being unhappy with the result, when a few extra bucks would have gotten something decent. If the difference is only a little bit, save a little longer and buy the better made product that lasts longer. No matter what you’re spending, even if it’s $5 for a can opener, you can’t afford to throw away money on something that’ll break in a few months. A few of the answers can get ridiculous (Aeron chairs? I wish!) but many of them are very interesting to read.
  • These shuriken magnets are cool.

Today’s video: a camera that poops out photos.

December 7, 2008

link adump

Filed under: linkdump — dalvenjah @ 1:05 am

Current Mood:Sore emoticon Sore & Tired emoticon Tired

Tonight we bowled. It was fun.

Links:

Today’s video is a poem on the impotence of proofreading, by Taylor Mali. (via VideoSift).

December 6, 2008

linky dumpy

Filed under: linkdump — dalvenjah @ 1:53 am

Current Mood:Exhausted emoticon Exhausted & Tired emoticon Tired

Links for tonight:

  • Easyweb is a French company that uses (bright) laser projectors to project spectacular 3D graphics and imagery on buildings, using building features in the presentations. Their six minute portfolio video is absolutely amazing; just sit back and enjoy it. Via Reddit.
  • Funny comic for today: Saturday Morning Breakfast Cereal. Via Digg.
  • Here’s a lovely concept — a cuckoo speaker (which is probably not a clock). Via gizmodo.
  • Adobe and University of Washington put together an interesting tool called Zoetrope — sort of like a visual WayBack Machine. MIT Technology Review put up a video about it, and Gizmodo did a quick writeup.
  • Sony’s released specs on their Cell-CPU-based server called Zego. Could be an interesting change from x86, especially for visual processing — and might give Cray a run for its money.

Tonight’s video: Real life Mario Kart! (via everywhere)

December 5, 2008

trying to get up to speed again linkdump

Filed under: linkdump — dalvenjah @ 1:31 am

Current Mood:Recumbent emoticon Recumbent & Tired emoticon Tired

Trying to get up to speed posting again; here’s a small linkdump.

And for today’s video, via Super Punch — what if the three wise men were RPG players? (Originally from For Tax Reasons.)

November 16, 2008

weekend linkdump

Filed under: linkdump — dalvenjah @ 1:30 am

Current Mood:Thirsty emoticon Thirsty & Tired emoticon Tired

Going to try and make a pie crust with cream cheese instead of butter or shortening tomorrow. Maybe also brown sugar instead of normal sugar. And if that turns out well enough, form it into little tartlet shells with yuzu curd in the middle. Wish me luck.

Beyond that, mostly photo fun today:

Tonight’s video — violinist Paul Dateh and a DJ Inka One from LA making really impressive violin-and-hip-hop (ish) music. It’s really, really impressively good, especially when they get further into the medley. I only dabble in hip-hop listening, but I’d buy their music.

November 13, 2008

small linkdump

Filed under: linkdump — dalvenjah @ 8:14 pm

Current Mood:Exanimate emoticon Exanimate & Tired emoticon Tired

Not much tonight. I had to get up unpleasantly early today, so a quick post, dinner, and bed for me.

Here are things I found:

And for tonight’s video, we have a toddler who doesn’t appear to be quite sure what’s happening, but he and the crowd are having fun:

November 8, 2008

long-time-since linkdump

Filed under: linkdump — dalvenjah @ 2:06 am

Current Mood:Exanimate emoticon Exanimate & Tired emoticon Tired

Okay, I got sick, and slacked on posting. I think I’m better now. Even the lingering cough is mostly gone.

Meanwhile, we have a new president-elect (yay!) and weather that’s starting to look more wintry.

Here are a few links I’ve stored up:

And finally, a song in Polish. Not sure what it means, or why. But it’s catchy.

October 11, 2008

a question for the economic smart people

Filed under: Politics — dalvenjah @ 6:09 pm

Current Mood:Sick emoticon Sick & Curious emoticon Curious

Okay, so I’ve been keeping up on the coverage of the economic disaster we’ve been having by reading The Consumerist and listening to This American Life, and trying to catch up on NPR’s Planet Money. And I’ve got a question, but I’m not sure where to ask it.

The problem as I see it is that we have a bunch of banks that are exposed to unknown risk by having sold credit default swaps and mortgage-backed securities. Nobody is able to say how much each bank or other organization is worth because while you have the list of assets that do have a value on them (standard stocks, buildings, equipment, whatever), you then have these other lists of assets that nobody can assign a value to because:

  1. for the credit default swaps, nobody knows who’s going to go under next so nobody knows if a credit-default swap that was sold for $10 million might require a payout tomorrow of $1 billion or more, and
  2. for the mortgage-backed securities, nobody really knows which mortgages are low-risk and which aren’t.

The way I see to resolve these items, while probably not easy or attractive for anyone involved, is for each bank and investment firm to drop their drawers and expose everything. Every credit-default-swap exposure, every investment, every mortgage they offered, every little piece of land and equipment they own needs to get published. Giant text file, giant spreadsheet, whatever. This will expose trade secrets and probably other things that each organization would probably rather remain unscrutinized, but at this point it’s either do this or the organization may not survive to exploit those trade secrets.

I can’t find the reference now [update: here's one, about the Reconstruction Finance Corporation], but I seem to remember reading that in the 1930s after the bank runs of the late 20s, the US government set up a commission to do a full audit of every bank, where every bank was laid bare to this commission and either certified solvent or not. That sounds like a good start.

If not done by the government, then maybe it can be coordinated by the Treasury and someone can set up a huge Amazon Mechanical Turk job or something. Imagine that — “Save the economy! Read two pages of this bank’s financial statement, add up the numbers, get paid ten cents, and help certify these banks!” The best reference I can find is from the New York Observer, in 2002, after the Enron scandal, calling for a Board of Audit. Yeah, it goes against the grain of every self-respecting capitalist who worships at the altars of Reagan and Thatcher, but I ask you, where is your god now? Oh right, he’s prolonging the crisis by randomly dumping wheelbarrows of money at your doorstep.

At the very least, someone needs to be going through all the mortgages that make up these mortage-backed securities and doing the due-diligence that should have been done in the first place. Pull all the paperwork, call everyone up and ask for paystubs and tax returns, run the credit checks, and assign each mortgage a real risk value. Then, at least, you’ll know how many loans were worthless, and how many were real loans to people with the means to pay them back.

So if these are the ways out of the mess, why isn’t anyone doing it? Maybe things aren’t quite bad enough; but if you have roaches or flour moths in the pantry, the only way to get rid of them is by pulling everything out, cleaning the pantry, closely examining everything you’ve got, putting the bad items out with the trash, and putting the clean items back in the pantry. Only then will you get rid of the pests, and there’s no other way to do it.

I realize it’s not my industry and I don’t have any real connection to the financial world other than hoping I (along with everyone else) don’t get screwed by what goes on with it, but it seems like most folks are just sitting with their heads in their hands and hoping that the badness will somehow blow over and get better. I don’t think that’s the answer, and while right now it seems like this might help, I’d love to know how I’m wrong.

sick linkdump

Filed under: linkdump — dalvenjah @ 1:18 am

Current Mood:Sick emoticon Sick & Tired emoticon Tired

Yugh. So this week I’ve been slowly succumbing to an actual being sick — the flu or something.
Today it got to the point where I just had to sleep it off, and I do feel better for it.

Some links I’ve been collecting slowly over the week:

Via I have seen the whole of the internet, the world’s worst movie chase scene, ever.

And in keeping with the 70s theme, via YesButNoButYes, a Japanese commercial for MANDOM, starring Charles Bronson.

October 3, 2008

alink adump

Filed under: linkdump — dalvenjah @ 12:11 am

Current Mood:Tired emoticon Tired & Exanimate emoticon Exanimate

This week has been busy. Here’re more links:

Also via Ben Fry, a short video on the history of predictive text swearing.

And a lovely ad for the Discovery channel; the song makes me happy every time it plays.