Resolved Time Machine External Backup disk problem

[T0mdaB0mb]

Hello all

This is my first post on MR (long time reader) because, cocky as it may sound, this is the first problem I have had with my Mac that i haven't been able to fix (with help from forums and such, of course). After searching around on the forums, both here and Apple's discussion threads, I have yet to find a solution. I apologize if a solution to my problem has already been posted and I just haven't looked hard enough, in which case please direct me to it and i will promptly delete this thread. But without further ado, here is a copy of my post on Apple's discussion threads (cuz I'm lazy):

Hello all

Recently, my external backup disk (a 750 GB WD My Passport) that I use with Time Machine has been acting up. At first, it wouldn't show up on the desktop, but was being recognized in Disk Utility (with the "Time Machine Backup" partition greyed out). After multiple restarts and unplugging/replugging the hard drive, I finally got to be properly recognized, i.e. it showed up on the desktop with the proper Time Machine hard drive icon. So I thought the problem was gone and started a routine backup. However, Time Machine returned an error:

"Unable to complete backup. An error occurred while creating the backup folder."

I search the forums, and followed the advice here: http://web.me.com/pondini/Time_Machine/C10.html

I tried repairing the disk, but DU couldn't repair it:

Verify and Repair volume “Time Machine Backups”
Checking Journaled HFS Plus volume.
Detected a case-sensitive volume.
Checking extents overflow file.
Checking catalog file.
Incorrect number of thread records
Checking multi-linked files.
Checking catalog hierarchy.
Checking extended attributes file.
Checking multi-linked directories.
Checking volume bitmap.
Checking volume information.
Invalid volume file count
(It should be 3991498 instead of 3904049)
Invalid volume directory count
(It should be 678218 instead of 673790)
Invalid volume free block count
(It should be 9588404 instead of 11784378)
Volume header needs minor repair
The volume Time Machine Backups was found corrupt and needs to be repaired.
Volume repair complete.Updating boot support partitions for the volume as required.
Error: Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.

So now I'm still following the advice on the above mentioned page by posting on here. Any help at all would be greatly appreciated. I am using a 2010 15in 2.66 i7 MBP, if that makes a difference, although my guess is the problem's with the harddrive itself. I think there may have been one time about a month ago when Time Machine stopped responding (or something like that) which forced me to pull out the harddrive, possibly corrupting the data. But I'm not sure, and I do recall making at least one successful backup after that. Well, actually TM confirms this: "Latest successful backup: 5/27/11 at 11:51 PM". So I have no idea what's going on. Again, any help would be appreciated.

To which I added:

It might be worthwhile noting that, apart from with Time Machine, the disk appears be working fine. That is, (as mentioned) it appears on the desktop and Finder sidebar with proper TM icon, I can access the files, I can write to it, I can create folders (which Time Machine seems to find itself unable to do), etc. That's why I tohught the problem was fixed at first (evidently it's not). It's only when I do "Back Up Now" on the TM icon on the menubar, that the error came up. And of course the multiple errors thrown out by disk utility... Perhaps the fact that it's only not working with Time Machine can shed some light as to which parts of the disk are corrupted?

And now, literally as I was just typing, I swear, Time Machine threw another error at me as I was trying once again:

"The problem may be temporary. Try again later to back up. If the problem persists, use Disk Utility to repair your backup disk."

Too late to worry about that now! but yeah, as in the post, I'd greatly appreciate any help. Cuz I'm really confused please bear with me as i'm still learning the ropes here.

 

[smirk]

I had this type of error before on a Time Machine repository as well. I'm surprised that Disk Utility can't repair it, though. If you own a copy of Disk Warrior you may want to give that a try. Also, I wonder if there's any way Time Machine itself is interfering with Disk Utility's repair attempt. Perhaps you could turn Time Machine off to see if Disk Utility has better luck. And realize that it sometimes takes several Repairs until it gets a clean bill of health.

Out of curiosity, is there a reason that drive is formatted with a case sensitive file system?

 

[T0mdaB0mb]

Thanks for your response

From what I heard, it's not worth buying Disk Warrior if there's only a slim chance of it actually being able to repair the disk. Also, I'm pretty sure I turned Time machine off in Sys Prefs when I tried the repair. But I'll try again, or as you suggest, try again several times.

I'm not sure about the fact that it's a case sensitive file system. After some googling, HFS+ is Mac OS Extended, while HFSX is Mac OS Extended, Case sensitive. So I guess it's formatted to HFSX, is that correct? In any case, like most hard drives, it was bought formatted as NTFS. When I plugged it in the first time, OS X offered to format it for me, and as I recall there weren't any advanced options for what type of file system. Typical of OSX, I'd say, as long as "everything just works". Which it did, so I didn't put any more thought into it.

If all else fails, I think I would just format it completely and re backup everything, since my Mac is working fine. Would you suggest I don't format it as case sensitive this time? What's the difference? I just want to make there is no hope of repairing it first, because, like I said, the drive otherwise appears to be working perfectly fine. I've also got other stuff on the drive (50GB+ total) that I don't really want to move around.

 

[T0mdaB0mb]

Fixed!

Ah, yes! Just tried repairing disk again with TM turned off, and it worked! Backup also ran without problems. Thanks for your help. Guess it's just one of those things with computers that can't really be explained.

I do have one question, though: what exactly is the difference between HFS, HFS+, HFS case sensitive, and journaled? Not that I'm in any hurry to reformat my disk, now that it's working again.

Thanks

 

[smirk]

Hey, that's great that you got it fixed!

HFS is an older file system, let's say it's like FAT on Windows.

HFS+ is the current "modern" file system, like NTFS.

Case sensitive means that "IMG_1000.jpg" and "IMG_1000.JPG" are considered two different files and could both exist in the same folder. This is not the norm with OS X; case insensitive is the norm, which means that the OS ignores the case of filenames. For drives connected to a Mac, at least for the boot drive, I think Apple recommends using case insensitive unless you have a specific need otherwise.

Journaling is a way that the file system helps stay in a consistent state. It records in a file all the transactions it's about to make prior to writing out the actual data to the drive. Then if it gets interrupted, such as if the power shuts off in the middle of a write, it can undo the partial transactions. For example, say you were in Word and were saving a document when the power cut out. Part of the word document was saved but not all. Further, the table that lists which parts of the disk are in use could be out of sync with reality, because the power cut out before it had a chance to update it. With journaling, the next time you boot up the OS will realize that something didn't get closed out properly and it will undo the partially-written data and get everything back in sync. Your Word document still isn't saved -- that data is lost -- but at least the disk is internally consistent. That's just a basic example and probably isn't 100% accurate, but you get the idea. Journaling is good.

I don't know if it's warranted or not, but I do a disk repair on my Time Machine repository every couple weeks as a preventative measure. I've lost the entire Time Machine backup before, and in reviewing the logs I saw that a problem occurred after a backup and then got worse with each successive backup, to the point that it couldn't be repaired.

 

[T0mdaB0mb]

Thanks for all your helpful replies

So, would you suggest that for the next backup disk I buy, I just format it as case insensitive? In what situation would someone want it to be case sensitive? Sorry for all these questions.

I think I'll take you're advice with repairing it every once in a while. Better safe than sorry!

 

[smirk]

You got it, format it case insensitive. People always want us to be sensitive but in this case you probably don't want it.

I'm not totally sure when you'd want case sensitive. Maybe if you shared a lot of files with another Unix or Linux system that had a case sensitive file system.