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TOPIC: Ext HD fails to mount, fails tests, but Time Machine can restore files from it

Ext HD fails to mount, fails tests, but Time Machine can restore files from it 29 Dec 2016 04:40 #7959

MBPro 8,2 — OS 10.8.3 — TTP 6.0.8

Time Machine alerted me it had't been able to BU on this HD.

Here's what TTP Volume Structures looks like: "Validation Error"
Volume Rebuild = "Rebuild Error encountered"

I did a surface scan on the HD: not a single bad block!

DU says:
"Verify and Repair volume “MahBouk”
Checking file systemChecking Journaled HFS Plus volume.
Checking extents overflow file.
Checking catalog file.
Invalid node structure
The volume MahBouk could not be verified completely.
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."

In verifying the drive (not the volume), DU says:
Verifying volume “MahBouk"
Checking file systemJournal need to be replayed but volume is read-only
Checking Journaled HFS Plus volume.
Checking extents overflow file.
Checking catalog file.
Invalid node structure
The volume MahBouk could not be verified completely."

I seem to remember a comment from one of these utilities about ownership of the disc, but disc permissions did not clear that up.

Meanwhile, TM can enter the disc and successfully restore a fine. I checked this out with a folder containg an audio CD's file. Perfect playback.

Any suggestions?

TIA
• MacMini 6,1 • 2.5GHz Intel Core i5 • OS 10.8.4
• MBPro 5,5 2.26Hz • OS 10.6.8
• two 2TB FW800 ext HDs (WDC MyBook Studio)
The administrator has disabled public write access.

Ext HD fails to mount, fails tests, but Time Machine can restore files from it 29 Dec 2016 04:53 #7960

Thanks for your clear and detailed report.

The node structure of the disk directory has two kinds of nodes. Index nodes point to other index nodes, until an index node points to a leaf node. The leaf node points to a piece of a file, called an extent.

The invalid node structure may pertain to only a single file or folder, but Time Machine is not going to let you make further backups to a volume with a disk directory error. The rest of the files and folders are the volume would be able to be located and read, hence the result of your experiment.

If neither Disk Utility nor the Volume Rebuild tool of TechTool Pro can repair the disk directory, you should erase the volume and start a new Time Machine on it. For a disk directory to be rebuilt by TechTool Pro, the disk directory files, the Catalog B-Tree and the Extents B-Tree, must each be able to be held in RAM. That is not likely to be possible with a Time Machine volume containing many backups, or a small number of backups of a large source volume.

Time Machine volumes are extremely complex. If you have 40 backups on a Time Machine volume, there may be only one copy of a particular file, but there are 40 disk directory entries for that file, because there has to be a pointer to it for each of the backups. In my experience and reading online, Time Machine gets better with later versions of OS X. I used to have to start over every few months, due to irreparable disk directory damage. My oldest backup was over a year old this August, until i decided to start again because I decided to replace the drive containing the Time Machine volume. (There are ways to migrate a Time Machine to another volume, but I chose not to do that).
MicroMat Inc
Makers of TechTool
Last Edit: 29 Dec 2016 05:00 by micromattech3.
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Ext HD fails to mount, fails tests, but Time Machine can restore files from it 29 Dec 2016 12:47 #7961

Right back atcha for the clear and detailed answer. No I won't lose much by starting over, and I figured that might be the case. Two follow-up questions:

1.) About the RAM available (and needed for a volume rebuild)… This MBPro has 8GB RAM (I'd has to look up whether that's the max). What can tell me the total size of data ("directory files, the Catalog B-Tree and the Extents B-Tree") for this particular HD (used exclusively for TM). (And does RAM need to contain all of these simultaneously, or just any of these for one particular phrase.) This is just so I can keep an eye on where this volume is, in terms of the above safety margin.

2.) It occurred to me that while this external was the BU for the internal and a second smaller external (250GB), I should really be setting up a TT Protection Directory BU on one of these discs, just for this situation. Y/N?

and 3.) "In my experience and reading online, Time Machine gets better with later versions of OS X"
This laptop's internal actual has two volumes, one for 10.8 and the other for 10.11. (All three of my machines are set up this way, for handling both legacy and current release apps.) I recently upgraded to TTP v9, but have yet to install it. Would it be smarter to set up TM and TTP on the 10.11 volumes, to take advantage of the later versions of the utilities? Realizing that they'd only be able to do their duty, when booted up in the Capitan volume…

(More questions than a 4-year-old…) TIA,

mrbl
• MacMini 6,1 • 2.5GHz Intel Core i5 • OS 10.8.4
• MBPro 5,5 2.26Hz • OS 10.6.8
• two 2TB FW800 ext HDs (WDC MyBook Studio)
The administrator has disabled public write access.

Ext HD fails to mount, fails tests, but Time Machine can restore files from it 29 Dec 2016 14:34 #7962

1. The was a free command line utility called hfsdebug that could tell you the size of the disk directory files Catalog B-Tree and Extents B-Tree. It was superseded by an $80 version called File X-Ray, which appears to have been abandoned. I do not know of any way to determine the size of the two files, which have to be simultaneously held in RAM. In many cases, repairing the disk directory of a Time Machine volume is not possible.

2. We do not recommend using TechTool Protection for the Time Machine volume. The files it creates would be too large, because the Disk Directory of the Time Machine volume is relatively very large.

3. Yes, if you run Time Machine after rebooting from the installation of OS X 10.11, I think you would have longer times between unrecoverable errors on the Time Machine.

I think it is clear that at least one of one's backups needs to have older versions of files, in case a file, such as a database, is corrupted when you save changes and quit the application, and you do not know about the corruption, leading to the file in a clone backup being replaced by the corrupted version. On the other hand, relying solely on Time Machine is not a good plan. There is a good overview of backup strategies in this article:

tidbits.com/article/15746
MicroMat Inc
Makers of TechTool
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