OS X - Hard drive copy doesn't match.

January 22, 2005 2:10 PM

OS X stumper: My internal boot drive (160 GB) "info" reports 12.4 GB available, 136.63 GB on disk. A bootable (120 GB) clone shows 55.42 GB available, 55.24 GB on disk. I've run Disk Utility and Disk Warrior, repaired and rebuilt and the report persists. (I checked the disk used with "WhatSize" and, while I've not done the math, the rough aggregate of disk used appears to be more in line with the clone, which is what I expect. I am not sure when this apparent mis-reporting began but I know it was recently.) Googling has failed me. What is going on and how do I fix it?
posted by Dick Paris to computers & internet (14 comments total)

Have you checked the format? Sounds like your internal drive might be formatted as Mac OS Standard instead of Mac OS Extended.
posted by dmo at 6:18 PM on January 22, 2005

Two things to remember:

1) Drive sizes are advertised as millions of bytes (1,000,000), but computer calculate a megabyte as 2^20 (1,048,576)

2) The file allocation table that stores the location of your files takes up a fraction of the disk. The larger the disk, the larger the fraction.

In short, there doesn't seem to be anything wrong with your drives at all.
posted by Freon at 6:24 PM on January 22, 2005

Your "120" GB drive is correct, for the mathematical reason Freon (1) states.

Re: your 160 GB drive: check out this article. This 137 GB limit is a known issue with what is called 48-bit LBA. Basically the drive has to have been *formatted* under OS X 10.2 or later, and the hardware also has to be able to see it.

A little more info on the above - what's your hardware; when was this drive first formatted - might be useful if seeing this article doesn't answer your question.
posted by ikkyu2 at 6:28 PM on January 22, 2005

Freon - Wait a sec, nothing wrong with his drives when one says it's half full and the other says it's full? Are you bonkers?
(Aside: I think that some people are misunderstanding the question, the problem being that you have one non-problem (the 160 gb drive not adding up to 160 gb) and one potential problem (running out of space on the larger drive))

My only contribution, if the internal drive is working fine and is reporting things properly, is that you might have your allocation-block size set to something large.
One of the settings when you format a drive is that you can format it into blocks of x size. 2048 bytes is usually the standard these days, although I sometimes see larger. However, if you have a file that is 2049 blocks, it will take up two blocks ... taking up 4096 byes, and that extra 2047 bytes can't be reclaimed for anything else.

So if your main drive has an excessively large file allocation size, 8096 bytes or something, and you have a bazillion tiny files (which *nix's like Darwin tend to), you're going to run out of space sooner than you would otherwise. This is my suspicion if everything's running properly.

The cure is to back up your data and reformat your 160gb drive. Make sure you select an allocation block size of 2048.
posted by SpecialK at 6:31 PM on January 22, 2005

I checked the info on a ReadMe file on my hard drive (20gb in this example, your numbers will be different based on capacity) and concluded the following: when a hard drive is formatted OS X for HFS Extended, it breaks it down into 4kb blocks. If you have a file that's only 1kb, it still has to be written into a 4kb block. That's why when you look at the "Used" capacity when you Get Info on the hard drive you can see two dramatically different numbers. The first number (the one not in parenthesis) and the Available should add up to something pretty close to the total formatted capacity.
posted by glyphlet at 6:38 PM on January 22, 2005

Sorry, not very precise was I... SpecialK is on to me.

The disks are both have journaling on and are formatted Mac OS X extended.

I'm not questioning the "real-size-does-not-equal-the-actual-space" math, the problem is that one drive is a clone of the other -- done last just today in fact -- a completely new clone to help with this problem and pending the possibility of reformatting the start-up disk.

As I said, the condition appeared recently. While I can not pin down a date, I do know that a few weeks ago the report was in line with what I expected for the internal (160 GB)drive. I've not added any out of the ordinary masses of data since.

The machine is a dual 2GHz G5. Been running like a top since new (over year now). Going to read ikkyu2's link now...
posted by Dick Paris at 6:43 PM on January 22, 2005

Oh. Running 10.3.7 with 2 gig of ram.
posted by Dick Paris at 6:45 PM on January 22, 2005

More info from Disk Utility... the posts so far prompted me to look deeper and see things I'd not seen before:

On the start-up drive (called Braeburn); Number of Files :372,436, Number of Folders: 67,815

On the clone (called Orchard); Number of Files: 266,164, Number of Folders: 57,920.

What on earth are those 106,272 other files? These? Deleted from CCC? (Screen shot from Carbon Copy Cloner)


posted by Dick Paris at 7:02 PM on January 22, 2005

Sorry: I read your addendum and re-parsed, and I see that I'm way off the mark here. Feel free to ignore my previous.
posted by ikkyu2 at 7:07 PM on January 22, 2005

I think I found it. I just don't know how to deal with it. I used Cocktail to show invisible items and have been scrolling and comparing the two drives. In /Volumes I have two additional "copies" of Orchard. When I was creating a new clone, I erased that drive twice (due to an error first time 'round using CCC and then trying to run-down a problem with getting a successful clone. (It turns out it is a bug involving having an iSight plugged in when running CCC.)

So can I just delete those copies? Syncing the clone and giving it a whirl.
posted by Dick Paris at 7:43 PM on January 22, 2005

So far so good. Braeburn is back down to 57.03 GB. We'll see how things go tomorrow with a log-out. Feeling sleepy now...

Tha's for the kick in the pants, everyone. It might look like I hepled myself but I certainly could not have done so without you.
posted by Dick Paris at 8:06 PM on January 22, 2005

Hey, Paris, as an aside, are you a prof or student at Shep College? One of my bestest friends in the whole wide world lives there and graduated from there. You might have known of her as the cartoonist behind Ramblers. Beautiful town you live in.
posted by SpecialK at 8:31 PM on January 22, 2005

The swap files (/private/var/vm/swapfile* in your screenshot) can get pretty huge if you don't restart occasionally. This, and a few of the other files that CCC does not copy by default, could account for that missing space.

You could try using RsyncX - I work with the guy who got this free app working under OS X, and it really is a great way to do backups (although the GUI is slightly trickier than CCC).
posted by sluggo at 10:06 PM on January 22, 2005

Er, Tha's+nk=Thanks! I've looked at RsyncX briefly sluggo but will check it out again. CCC has always been good to me and saved my ass not for boot issues but for stored preferences -- long story.

The offending files were definitely not those deleted on the target by CCC -- not nearly large enough. I'll need to poke around more at the Bombich forums to see if I can learn something more about what happened.

SpecicalK: My wife went to college in Shepherdstown, worked at "The Bank" for years and it is where we wed.
posted by Dick Paris at 3:00 AM on January 23, 2005