[Macpartners] Re: Macpartners Digest, Vol 17, Issue 4

[John C. Welch]

On 10/8/04 1:43 PM, "Kerem B Limon" <k_limon at MIT.EDU> wrote:

>> If it's a dead partition on the same drive, but you can get to your boot
>> drive, the LED says "Stuff is happening", but since you can use your boot
>> drive, you kind of expect that, since you're using the drive.
> 
> Again, more useful information available with an HDD LED. Obviously I have
> booted. I am having trouble accessing stuff on this partition--hey, the HDD
> LED
> is getting stuck solid on! Maybe it's not my software, there's something on
> the
> partition there.

Or maybe not. It isn't telling you anything but that there's activity. You
don't know why. You don't even know what kind. Could be meat, could be cake.
A light is telling you...MeatCake.

> 
>> 
>> If it's a dead secondary drive, that's simple too, it won't mount. The light
>> is ONLY telling you that *something* is happening. Not if it's good or bad.
>> However, a bit of observation will tell you that. If the drive head motor
>> has completely died, the light will be useless since a) you won't be able to
>> access the drive *anyway* and the light will only tell you that nothing is
>> happening, since they don't tell you that the spindle motor is okay, but the
>> head motor is dead and gone.
> 
> Again, I've booted I presume, and we can't access secondary drive. The
> secondary
> hasn't mounted and when I try to use a disk mounting tool or partitioning
> utility, I cannot see the drive and/or the LED gets stuck if I see it and am
> having trouble accessing it. I know what/how it's failing.

No you don't at all. You know exactly what you know without one. That you
can't get to the drive. You don't know if it head crashed, because even with
one of those, assuming you can't hear it, you get activity. You don't know
if the VBM is hosed, your b-trees are corrupt, or if the IDE/SATA cable is
shorting/worked it's way loose. All you know is that there is some form of
activity, but you have no idea what it is.


If the only diag you have is a binary light, it's really not going to tell
you much.

> 
>> 
>> In Janet's case...she can tell the drive is running, since she booted off of
>> it. What is the light going to do in this case...."Yes, just in case you
>> didn't trust the booting bit, your hard drive arm is swinging back and forth
>> like Britney Spears' hindquarters".
> 
> She can tell if it is something to do with the hard drive or software/OS (i.e.
> media vs. software). She opens the folder, the drive starts accessing
> vigorously (perhaps not as much as Mrs. Spears) and then gets stuck on. It's
> probably a corrupt sector coinciding with a bit of a file that contains
> directory/index info or some metadata stream that gets accessed when the
> directory listing is done.

Or, it's a corrupt file in /Library/Preferences, which would affect all
logins. Something hosed in the DirectoryServices folder will cause ALLLLllll
kinds of grief. 

Or, there's a corruption in nidb, so the finder can't tell what any user is
allowed to do.

On and on, and on. These are all problems I've seen by the way. None of the
disks had bad structures. Light would have done no good.

> On the other hand, the drive accesses, the freeze
> does happen, but HDD activity ceases--it's a hung process or thread, most
> likely, due to perhaps some corrupted binary.

Or the spindle motor just died. Or the arm motor. Or maybe the power cable
to the drive is bad. Or there's a process that is just using a lot of CPU at
the moment. QuickTime Player will do this. So will Snapz Pro on startup. If
the authentication frameworks are having a bad day, you're going to see this
a LOT. Safari will cause this kind of behavior too with the right web page
problems

> Or perhaps the LED goes into
> overdrive, flickering wildly and thrashing--perhaps the software is trying to
> do the 'wrong thing'? Is it trying to access something unnecessarily? Is there
> something else running?

Perhaps you're recording audio. Perhaps you're ram bound and you're in the
swap a lot. Perhaps you have a compile/build/install going. Perhaps there's
some damned prebinding thing going on.

Again, the light is only telling that *something* is happening. It's not
telling you what or why. Only that certain mechanical processes are going
on. Nothing more, nothing less.

> 
>> 
>> When hard drives weren't a requirement for function, the light made sense.
>> It makes sense in a headless situation, since you may want to just visually
>> check without logging into the machine remotely.
>> But when you're booting off the drive, it's redundant and silly. If you have
>> your CPU unit out of immediate visual range, it's not immediately useful
>> anyway.
> 
> You've narrowed down the case to a desktop or workstation, obviously not
> headless. With cable limitations the way they are, how far from visual range
> can the computer be, anyway? Certainly not far with the case of an iMac! And
> since when is it more troubling to take a peek at the box those rare (ahem)
> times you run into trouble as compared to opening up your box and trying to
> make sense of diagnostic LEDs?

Again...you see the LED..it tells you something's happening.

But you can't even use the flicker rate as an indication, unless you're
intimately familiar with normal behavior in various situations.

I'm not saying they're totally useless, but I haven't used them regularly in
over 7 years, and I haven't missed them much. They're more of a
"oooooh...LIGHTS"

Quite literally, that's why the Xserve and the Xserve RAID have them. They
make people feel good. They're useless diagnostically.


>> If your display or screen is on the fritz, you're probably not doing much
>> with the machine at that point.
> 
> "display/screen" here in context meaning the GUI/UI is stuck or not responding
> and not the hardware itself failing per se.

But that can happen while having nothing to do with the hard drive. If you
have a 1999 PowerBook G3 with a first Rev memory controller and >64MB of
RAM, I can make it happen on command. The memory controller had a bug. A
hard drive light was useless in that case.

john

-- 
"Cluster bombing from B-52s is very, very accurate. The bombs are guaranteed
to always hit the ground."
USAF Ammo Troop.