This Nerd Heard…

So we shipped a whole bunch of products out into the field that use LSI raid cards.  The controller cards have cache on them, as do the drives.  The drive cache was left on and it ended up causing a bunch of headaches for us in the field.  Obviously it is bad to cache on both the hard drive and the controller.  If the drive loses power before it writes its cache to disk, the controller will think everything is ok when, in fact, the cached data was never written out.  It has caused drives to fail in the field and sometimes arrays do not rebuild when a drive is replaced.

So, since I did the hardware abstraction layer, which interacts with the LSI cards through their “megalib” library, I was tasked with writing an application that would disable the drive cache on all of the hard drives.  The drives in question are SATA drives, but the LSI card makes them appear as SCSI devices to Linux.

In order to disable the cache, I have to send a command directly to the drives using a pass through function in the controller cards.  After finding some good resources on SCSI commands, I found it wasn’t actually a difficult task.  But the LSI Library’s pass through is somewhat confusing to me and not very well documented.  You pass in a CDB structure (command descriptor block) that tells the drive what you want it to do (in this case modify the drive cache settings). 

The problem being that I need to modify just one bit of an entire byte.  So I have to know the value of the rest of that byte.  So I sent in a command to read the drive information.  Using the serial output on the LSI card, I can see that it is reading the HDD configuration, but I see no change in the output with write cache enabled and disabled.

The pass through function provided by LSI requires you pass in a CDB which also has a pointer to memory used for input or output (depending on the command you send).  When I try to just set the first three bytes (which are all I should need to modify the drive cache), it fails. 

So, not only does it not seem to be reading the data properly, but it doesn’t seem to write it either.  Most likely, I’m doing something wrong.  But the fact that there is no satisfactory documentation, and that I have to wait to hear from one of their developers, kind of irritates me.

But, I cannot say a whole lot here because the code my work puts out almost completely lacks documentation.  I’ve written general classes to do some basic things only to be told by someone later that we already had a class written to perform that task.  Of course, I couldn’t have possibly known that unless I delved through our source.  The problem being that we have millions of lines of code!

Edit: I forgot, I was going to put some links to some great resources that I found.
This one from answers.com talks about all the different commands you might want to issue to a SCSI device.
Here is one from Apple that shows where the WCE (write cache enable) bit is changed.

Ok, here I am putting in a shameless plug for a friend of mine.  He wrote a time clock or time sheet program for windows.  You can find it here.

Alright, I’m not just putting it here as a shameless plug.  I think it is pretty cool.  He spent a lot of time and effort developing it in his free time.  What I find so remarkable about it is that he wrote it using pascal.  I thought it was an interesting choice.  I don’t know anything about pascal, to speak of.  I didn’t even have a class on it at school.  I’m not at all remotely interested in it as a language.  Granted that Delphi is still supposed to be pretty popular.  There are sites devoted to it.  But this friend of mine hasn’t had to do pascal programming at work for years.

If I had a lot of viewers, I’d probably get flamed for being so marvelled by the use of pascal.  But I guess it’s just a change in the wind, all programming languages tend to get phased out.  It’s sink or swim in this world.  I’ll likely have to learn some languages that I had never dreamed of some day.

Sometimes, when I listen to my coworkers talk about software, linux distros, etc, I wonder if I am really a computer nerd.  They talk about all these things that only seem to interest me mildly.  I’m always willing to talk to them about it, but never know as much as they do, and never am interested in learning a whole lot more.

I’ve worked on some interesting projects in the past that I have enjoyed.  I’ve worked on a Hardware Abstraction Layer (HAL), audio/video network transportation, code optimization, and administration tools just at my current employer alone.

They have, for the most part, been interesting projects.  The most interesting being the optimizing, and the HAL.

I’ve decided though that what I am most interested in is security, encryption, and other such things.  I probably am not good enough at math to develop or break encryption algorithms.  But, I think I need to start spending time getting more acquainted with these things that interest me.  Even if it never ends up aiding me greatly in a professional aspect.  I think it would make an interesting hobby.