Untimely disconnect of external disk drive, now I cannot mount it

Question

Untimely disconnect of external disk drive, now I cannot mount it

Many times I have inadvertently disconnected an external drive before "ejecting" it, a procedure that evokes a system warning but upon restart a result without consequence. The external drive remounts perfectly when reconnected. Now for the first time I find I cannot remount a disk that I inadvertently disconnected before ejecting it. Attempt at using palliatives such as "Disk Utilities" to

This disk is actually a second of two logical partitions on a single external disk. I don't see how this can make a difference, except in this case the first partition on the same external hard disk re-mounted without flaw.

I tried using Disk Utility to Verify and Repair volume. But Disk Utility responds "... can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files." There is now indication how I can use Disk Utility to do this. So what is to be done?

For example, I have routinely backed up my main internal disk to this external hard disk via Time Machine. But the destination for the Time Machine backup of my main computer is this very same external disk partition that I cannot remount! So it seems to me that, to "back up my files," would require me to read and write from this now disabled partition. I tried using TechTools in "recover files" mode without result since it also seems to assume that the target disk is mounted. Might I need to resort to "terminal" mode to discover how to remount this delinquent partition, or at least to copy files from the crippled volume?

Any ideas?

iMac (21.5-inch Mid 2011), Other OS, OSX Maverick 10.9.4

Posted on May 3, 2015 6:02 PM

Reply

Answer 1

May 3, 2015 6:10 PM in response to norman.chonacky

It sounds like this last you shut it down at the same time the system was doing a critical update to the disk drive. Since the critical update failed to finish it left your disk drive in a corrupt state.

Backing up to a partition on the same disk drive as your data is worthless as you have just discovered because you lost the disk drive, you lose both your data and your backup.

Sounds like it is time to reformat and reinstall OS X and start all over again.

Reply

Answer 2

May 4, 2015 11:28 AM in response to norman.chonacky

DiskWarrior might be able to help. http://www.alsoft.com/DiskWarrior/

Reply

Answer 3

May 4, 2015 12:21 PM in response to norman.chonacky

I appreciated the suggestion from dianeoforegon. I normally use TechTool Pro, but if I continued to be stuck I would have probably tried DW.

However, there has been a development and I should report it as a "solution" in case it is helpful to others.

The solution: I put the iMac to sleep overnight and when I brought it back up this morning ... voila, the icon for the delinquent partition was on my desktop! Game over. Let me tell you what I observed during this process and you can formulate your own conclusions.

Cause: This disconnect was accidental. I dislodged the USB connection. Since this partition on an external drive is where I store my TimeMachine datafile, my guess is that there was an automatic backup from iMac internal disk going on in the background that initiated the mess once contact was broken.
Symptoms: Running OS-X Disk Utility I was able to see the faulty partition's icon
Action: Selecting the DU button to mount the partition resulted in an error and a directive suggesting I try disk first aid.
Action:Selecting disk first aid resulted in error advising me that the partition was unrepairable and a directive suggesting I backup whatever files I could, then reformat and reinstall. This was not acceptable to me without further efforts and in retrospect was premature, bad advice.
Other action:I ran the repair utility TechTool Pro 7. Launching the tool Volume Rebuild I was able to see an icon for the (still) unmounted partition, select it, and run the directory repair without error. However, the partition icon was still grayed indicating it was still unmounted.
Reprise: Back to Disk Utility to try mount, which still failed.
Repeat: steps 5 and 6. No luck.
Truce: Put the iMac to sleep and myself as well. Bad dreams about losing all my four years of back data

After the morning epiphany, I did some retrospective thinking to try to explain the "inexplicable."

Speculation: I wonder if first reconnection the (accidentally disconnected) external drive might have initiated an OS-X resolution routine that is done automatically in the situation of ill-advised disk removal (my original "sin") in order to prepare the insulted disk for remounting. I have had many such USB device disconnects in my long Macintosh career and have always noticed a latency between device reconnection and remounting of the delinquent drive. I am speculating that this process requires a scan of the file(s) that was(were) implicated in the disconnect due to interruption of a device process at the time. The first partition mounted first, and was a very small piece of the 2-terabyte external drive. On the other hand, the delinquent partition was most the remaining space on the drive and contained this huge data file (the Time Machine database). Could it be that only my impatience and my distraction failed to recognize the signs of a resolution process on-going? What the disk needed was for the computer to visit morphos.
Moral of this story: Don't believe simple automated advisories from utilities that can't share your pain. In this case, my neglect was benign and just what a computer doctor might have ordered.

Reply

Answer 4

May 4, 2015 7:08 PM in response to norman.chonacky

It could be the process TechTool Pro was running took a lot longer than expected and while you thought the Mac was asleep the repair completed.

Whatever... we can be glad you got your data back. I would be looking for a good sale on a second external drive. It's always good to have a copy of your backup drive in case it dies.

Reply