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I'm often replacing user's hard drives (in Mac laptops, in my environment), and was wondering: how likely is the problem to be physical, and how likely is it to be logical?

I typically assume that the problem is physical, and that, if I were to reformat the drive and put it back into use, it will fail again, causing problems.

How can I tell if the problem is physical or logical? Is there an appropriate assumption to make? [On the Mac, I do run Disk Utility; on ocassion, it will show logical errors, but typically it will say the hard drive is okay, even if it is running very slowly and will not let me copy files off of it.]


Update: For my purposes:

  • a physical problem is when data can not be read from the drive or when the data read back differs from the data most recently written to the disk; the hard drive platter (or controller) no longer works
  • a logical problem is when a file or file system structure is written improperly; when data on the drive is corrupt--possibly due to power loss or a process modifying a file being terminated prematurely. While the drive itself is good, the files do not load up right, or the meta-data describing where the files are stored is not consistent.

By way of analogy,

  • a book with a physical problem has pages that are torn out, ripped, are wet or rotten or bitten, or came out of a printer that was running out of ink. It is anyone's guess if you can read something meaningful off the page.
  • a book with logical problems may have grammatical problems, poor sentence structure, or even just strings of random gibberish. You can read it just fine, but it doesn't make any sense.

In my mind, the differences is that a logical problem will go away with a reformat, but a physical problem persists.

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How likely? Depends on how rough your Macs are treated, I suppose...it's very likely if it can't find the system files after it landed on the floor. –  Bart Silverstrim Dec 11 '09 at 18:25
    
See below, answers highly depend on what you mean by "logical drive". If you mean filesystem errors see Bart's response. –  Dave Drager Dec 11 '09 at 18:31
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2 Answers

Physical and logical hard drives are in different domains. Physically, there is only one hard drive. Any "Logical" hard drives are just partitions on that physical hard drive. Therefore, if there is an issue with a logical hard drive, this is actually an issue with the underlying physical hard drive.

[As a slight aside, it could be cause by a bug in the underlying file system drivers but they are very mature and rarely have these types of bugs.]

So in that respect, you are correct in assuming that if you reformat the drive and put it back into use, that it is very likely it will have problems again.

Let me know if I totally misread your question! :)

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I was interpreting his "logical drive" as his version of filesystem layer problems, physical being...well, physical layer :-) –  Bart Silverstrim Dec 11 '09 at 18:24
    
I've added notes to my question to clarify what I was getting at; basically, by physical problem I mean the hard drive platter is failing, and by logical problem, I mean that files or filesystems are corrupt, but the drive itself is good. –  Clinton Blackmore Dec 12 '09 at 4:57
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Not sure about the Mac; on the PC I check using the Ultimate Boot CD and run their drive diagnostics.

I usually tell because when a drive is physically bad, there is a stronger vibration or as the drive resets. There are also log entries about device resets and read/write errors.

If it's a logical error then the drive utilities will normally repair them without further issues (if you repair it, rerun the check and it finds another swath of issues, then again, and again...you probably have a problem physically).

SMART status (also in the disk check utility, but there are some you can get for the Mac for free that monitor it in the menu bar) can give some indication of drive failure as well. The problem with SMART is similar to software memory checkers though; when it says it's bad, it's bad. When it says it's good, it might be bad.

My procedure? If there's a chance that the data in question or giving a problem arose because of something in particular that caused a crash...document corrupted after Word crashes, or bad entries on the filesystem after a hard crash...it's probably filesystem in nature. If there's no rhyme or reason and just failed out of the blue, I suspect it. If it's thunking or giving reset errors in logs, I throw it. If a full defrag of files gives the disk a workout (or a drive diagnostic checking every block) doesn't get it to go spastic, I suspect it's filesystem, not physical drive in nature...

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