Monthly Archives: March 2014

Inexplicably slow hard disks? Try disabling PIO mode

A baffling problem I came across recently was a server where copying between internal disks ran painfully slowly, getting around 3.3MB/s between internal SATA drives. Of the machine’s three disks, two were failing with huge numbers of ATA errors and bad sectors, so I pulled those out an ran test copies to and from the remaining system disk, with no improvement. Incidentally, to find out that the drives were failing I used a brilliant little tool called HDD Guardian which reads SMART monitoring values the same way smartctl does, just with a nice graphical interface.

It turns out the server had defaulted to IDE mode on the disk controller as Server 2003 doesn’t really contain any SATA AHCI drivers and you’d need a floppy disk to install them. In of itself this wouldn’t cause an issue, but when Windows detects multiple CRC errors on a disk transfer, it will reduce the transfer rate. Eventually the disk will become stuck in Programmed Input/Output or PIO Mode, which essentially means all data transfers must pass through the narrow CPU IO bus rather than going via system memory which chews up a lot of CPU time. There’s a lot more info on this topic at http://wiki.osdev.org/ATA_PIO_Mode.

To fix this, there are some instructions in KB817472 in the Microsoft Knowledgebase and some other instructions in this TechLogon article, neither of which fixed the problem. Since the server in question is a VM host and all the VMs were copied onto other systems anyway when the drives failed, I just reinstalled it with Server 2008 and the disks set in AHCI mode, which is cheating, but it made the problem go away.

Now my transfer speeds are back to normal, so I just have to replace the two 500GB drives with 4000 reallocated sectors. Drive magnets anyone?

Neat Video noise reduction test

A quick comparative test of the Neat Video noise reduction plugin, mostly because YouTube does its own noise reduction so I can’t host it there. You probably want this full-screen to see the effect.

Notice the slight noise increase on the left hand side, and more signficantly the herringbone pattern caused by RF interference with the composite video over the long (ish) cable run and the not great analog performance of the cameras anyway.

The source isn’t really going to improve at all as the equipment it runs through is very old, but the plugin has pretty much completely removed the noise!

My flight simulator experience

Today I got the opportunity to fly a Boeing 747-400! Cue cheesey grin in shoddy phone photograph:

Me in a 747 cockpit

OK, so it wasn’t a real one. British Airways ran a giveaway over Christmas and I was lucky enough to win one of three simulator sessions at the Cranebank training centre where BA train and certify their pilots. After a couple of emails and fighting my way through the rush hour traffic heading into London I dutifully showed up at a painfully early time this morning (8:15 is a dirty word among students!).

I was introduced to Andy who would be my pilot and instructor for the session, and ushered through a maze of corridors to the simulator itself. The simulators at Cranebank are full-motion, so they are basically a cockpit wrapped in screens, all supported on big hydraulic jacks that make it feel like real flight. The inevitable safety briefing followed and like everything in aviation redundancy was everywhere; in an emergency the simulator would ‘land’ and the access bridge would lower, and if that failed there was a ladder, and if the simulator angle stopped the ladder coming down there was a scramble net! Andy pointed out they’d never even needed the ladder before as the bridge had always worked.

By Denelson83 (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

Primary Flight Display (PFD) with pink Flight Director lines

Some years ago I learned to fly a Grob Vigilant motor glider and even made a solo circuit, so we went through the controls and what the instruments did fairly quickly, paying particular attention to some of the automatic systems that make these aircraft (relatively) easy to fly. One such system is the Flight Director, which means altitudes, headings and climb rates can be programmed into the autopilot panel and pink lines on the PFD tell the pilot where to point the plane.

We set up for a takeoff on runway 27L at Heathrow, and I immediately got confused as the conditions were set for early evening but I’d arrived in brilliant sunshine at 8AM, which just goes to show how realistic the simulator is. You could even see headlights from the cars driving along the A30 and M25 near the runway! I made a rather wobbly takeoff that just about stayed on the runway, then flew a couple of turns, climbs and descents to try and get used to the aircraft, it feels a lot more sluggish than the little gliders did!

The simulator set up for takeoff

The simulator set up for takeoff

Up next was the big one, landing again. Andy talked me through it and handled all the aircraft setup like flaps and landing gear, and after nearly missing the runway and going quite a long way down it before touching the ground, it just about worked out. Oddly I landed quite a long way down the runway on my solo glider flight too after completely stuffing the approach angle and speed. Still, what is it they say, a good landing is any one you can walk away from and even better if you can reuse the plane!

We reset the simulator to 12 miles out to try again, which is where things went a bit wrong. The autopilot was engaged and setup to capture the ILS (autoland…ish) at Heathrow and the flight freeze was released. The throttles immediately advanced to full power and the whole cockpit shuddered a lot while Andy said “I’m not really sure I like that vibration” as he hastily went for the freeze button again. We reset the simulator, reset some of the controls and changed some configuration, shut off the autopilot and autothrottle this time, and tried again with much the same result. I noticed that the engine power gauges are still sat at idle despite the throttles being in the middle, and it looked to all appearances like we were dropping straight down towards Clapham when Andy hit the freeze button again.

It turned out that above the power gauges the “REV” indicator was still on, showing the thrust reversers were still extended after the earlier landing. This shouldn’t be possible in flight and the lever won’t even move unless the plane is on the ground – for good reason too as it makes the plane fall out of the sky! To get them to close again we called another Andy who had set up our simulator session and he pulled all the flight management computer circuit breakers, positioned us back on the ground and let the reversers close, then reset everything again to clear the problem.

As a minor technical note, particularly topical at the time I’m writing this; there is a huge panel of circuit breakers above the pilot’s head in the 747, including two clearly labeled ACARS. For all the news media reporting on the tragic disappearance of MH370 and how detailed technical knowledge is needed to turn ACARS off in the 777, I think they need to check their facts as once in the cockpit you just need to be able to read and pull two breakers!

After a slightly more successful landing (well I landed at the right end of the runway) Andy showed me what a category 3 autoland looks like in thick fog. Imagine staring at a blank white sheet, until at 50 feet above the ground a runway materialises out of nowhere and a second later you hit it, hoping that the autopilot has set everything up properly!

Finally we went for a change of scenery and took off out of Geneva in Switzerland, climbing out towards the Alps before turning back for my neatest landing yet, in that I stopped in the middle of the runway even if I touched down quite a long way to the left!

We’d run out of time by then, but the experience was absolutely fantastic, and I’d like to say a big thank you to British Airways for setting up the competition, and to Andy C and Andy S for a great morning out.

How to fix a loose battery on Acer Aspire 5750

I’ve had my trusty Acer Aspire 5750 for a few years now; and with the addition of an SSD, from PC World of all people (there was a sale), I expect it to last for a while yet. On and off I’ve noticed it failing to resume, or just powering off at odd times and worked out the battery is loose, but up until now I haven’t been able to fix it.

Inside the battery compartment are a pair of plastic loops which are the catch for the release mechanism, and then there are fixed plastic wedges on the battery for the loops to snap into. It looks like one or both of them is on the edge of tolerance, so occasionally the battery would fall far enough to lose contact and power off.

A little bit of plastic to the resuce

A little bit of plastic to the resuce

The solution: Cut a tiny piece from a plastic card (I used an expired gift card) and leave it on top of the battery when it goes back in, and then pull open the battery release and push it down fairly hard – who’d have thought such an annoying problem would be so easy to fix!

Anyway, I couldn’t find anything on Google for it, so hopefully this helps somebody.

EDIT 28/08/2014:
Well it turns out that wasn’t a very permanent solution to the problem, it kept coming back when the bit of plastic fell out. In the end I bought a new battery from Amazon (one of these) which has actually fixed the problem, it doesn’t wobble anymore.