Thursday, May 26, 2011
So, I was brought into yet another high-key, holy-cow, we-just-have-to-fix-this, something's-wrong-with-your-product session a few days ago. After looking at the symptoms, my question was simple - "Have you checked disk performance?" When the response came in the negative, my immediate response was, "enable statistics, run Perfmon (this was a Windows platform), and retest." Well, the results hit my chat window yesterday:
Disk queue lengths are often misunderstood, so allow me a moment to explain. This metric simply reports the number of transactions that are waiting on disk input/output. There's no direct correlation to the SIZE of each transaction; you could have 5 transactions awaiting 1Kb each, 5 transactions awaiting 15Mb each, or anything in between. The important thing to keep in mind is that, back at the application layer, there's probably an executing thread behind each of those queued transactions. In all likelihood, there are other threads waiting upon those "pending disk I/O" threads...and you see where bottlenecks at this layer can create significant performance problems. In this example, the worst-case scenario (the peak disk queue length) showed over 4500 transactions awaiting disk I/O. In a word, ecch.
For the nth time, folks, it's all about disk I/O AS PERCEIVED BY THE OPERATING SYSTEM AND APPLICATIONS! This application happened to be running under a very high-powered VMware machine, with an equally high-powered SAN providing storage. When they looked at overall disk performance between the SAN and the VMware server, they saw "high throughput" and "low latency;" however, viewing the question from the perspective of the individual host OS presented a markedly different result (and definite "red flag").
Every OS/hardware vendor is in agreement that disk queue lengths in excess of 2.0 indicate I/O bottlenecks. I don't care what your SAN folks say, and I don't care what your virtualization folks say - check it out for yourself. At the OS layer, you can check these metrics with Perfmon (Windows) or iostat (Unix/Linux). If your average queue length is higher than 2 over a substantial period of time, you're suffering from disk bottlenecks. If you see peaks above 2.0 during particular activities (e.g. backups, particular server tasks, scheduled operations, etc.), then you're taking a performance hit there as well. This needs to be a part of every admin's "general health" dashboard - get on it!
Tuesday, May 24, 2011
It can be difficult, in some ways, to live "in the shadow" of a metropolitan area. It often seems that the "city schools" and "city teams" get the lion's share of media attention, and that smaller schools often get the proverbial short end of the stick. Well, Woodford County High School has been making some noise in academic circles over the last few years, and that trend has continued in the Washington Post's 2011 High School Challenge. WCHS came in at #567 in the Post's rankings of more than 1900 high schools across the nation; of Kentucky schools in the rankings, WCHS ranked #8. This comes on the heels of their placement in last year's Newsweek Top 1000, and shows that we're on the right track. To teachers, staff and students (3 of whom are my daughters - *grin*), I say "Well Done!"
Did your school make the cut?
Monday, May 09, 2011
Yes, it's another trip Down Under for free music. This time around, it's New Weird Australia that draws our attention. NWA is a non-profit initiative (supported, in part, by the Australian government) promoting "new, eclectic and experimental Australian music." Their latest sampler, "We Are After All Here," succeeds on all three counts. I'd recommend this compiliation on purely break-your-routine grounds, but several tracks stand out; my FLFs (First-Listen Favorites) are Horoscope from NO ZU, Camryn Rothenbury's Racing Across the Void, and Cannibal Cod by Desfontane.
If you like We Are After All Here, hit the "Compliations" link at the top of the page; you'll find several more samplers with which to feed your eclectic side...
Wednesday, May 04, 2011
OK, I admit it; I've always loved comics and comic books. My introduction to the medium came from my older cousins; whenever we'd spend an (otherwise boring, for me) afternoon or evening there, they'd take me down to the basement where they kept a decade's worth of comics. I immersed myself in Legion of Super Heroes, Doctor Strange and countless other titles for hours on end. Later, I read several of the titles my grandfather had printed during his career as a pressman for Fawcett Printing. Sure, recent years have seen the rise of other forms of comic art--notably graphic novels and manga--but there's still something special about a good old comic book.
Want to reminisce, introduce a young one to comics, or rediscover them yourself? Well, Free Comic Book Day is just about the best way to do it, and it's coming up on May 7th - this very weekend! FCBD is celebrated by comic stores across the US and Canada, as well as those in 40 countries around the world. Basically, it boils down to "visit your local store, get a free comic (or 2 or 3, and maybe a free figurine or ring...)," and it doesn't get much better than that! This will be the third year I've taken at least one of my kids out for FCBD, and it's always a fun time for us. There are 37 titles in this year's FCBD lineup, so your local store is bound to have something that tickles your fancy.
Check out the FCBD website, find your local participating store, and go get some free goodies!