External drives · bench notes · ADR-2025-2869
The Listing Was There. Nothing Behind It Was.
This customer’s two Macs (an iMac and a MacBook) could see the drive, but couldn’t do much with it. This resulted from the fact that, as she wrote, it does not automatically mount when plugged into my iMac or Macbook
. As a result, she'd developed a routine of manually mounting it, which worked, after a fashion. However, once the drive mounted on either machine, she found that the folders appear but will not open
. When she tried to open any of these folders (by double clicking), there was no indication of any contents. At this time, she hadn't used a repair utility or reformatted the drive, which is a large part of why this case ended like it did.
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What failed, and why.
A file system operates to keep two items separate. One item is the index. It contains the name(s) of the items contained within the file system, their date(s), etc., and a note of where the actual physical location of the item exists. The other is the actual item itself, wherever it may exist, out on the platter(s). If folders show on your screen but refuse to open, it indicates that the index has been successfully read, but that the actual contents referenced by the index have not. Therefore, the volume isn't empty or blank; it simply fails during the second step. Manually mounting shows similar results, but quieter. A Mac can mount a healthy volume by itself in a couple of seconds. When a Mac can’t perform this operation automatically, it implies that something under it is responding slower than the Mac can wait for. Each additional double click represents another series of retries against a mechanism that has already demonstrated unreliable performance.
What the bench did with it.
The order of the job →| Equipment used | Its work on this job | The reason for it |
|---|---|---|
| DeepSpar Disk Imager 4 | Zone-by-zone profiling of the read behaviour, then taking the copy with retry limits reduced. | Mapped the heads first, then imaged one face of a platter per pass, with every reset, timeout and the power itself kept under our own control |
| DeepSpar USB Imager | First pass included the caddy’s own USB board with no Mac in-line anywhere | Reads through the caddy's own USB board instead of going around it, at the rate permitted by the bridge |
| UFS Explorer Professional Recovery | Parsed the Mac volume from the completed copy. Pulled the folder contents out. | When other applications will not open it, this application will open APFS, ReFS, XFS, ZFS and Btrfs. |
What the bench did with it.
Find out what the slowness is
Here, the drive was not mounted, and none of its folders were opened or double clicked. Instead, measurements were taken of the drive. Read timing was taken across the entire surface of the drive, zone-by-zone. In doing so, a clear pattern emerged: large sections read at full speed, and then bands where one sector took hundreds of times longer to respond. These bands represent what was preventing the automatic mount from working properly. They also explain why her folders were visible at all, since the index resides in a section that still reads well, while a good deal of what it references doesn’t.
Take one copy, and keep the retries short
In such a condition, a drive has a finite number of reads available until it runs out. Each subsequent attempt on the same few sectors wastes some of these. Thus, the copy was taken just once, behind a write blocker. The number of attempts allowed per address was fixed ahead of time. Also, areas where response slowed down significantly were reserved for a final sweep. Sound regions were traversed at full speed. No previously responded-to addresses were asked again.
Open the folders here, not on the drive
Her folders were accessed via the copy, rather than by attempting to access them via the original drive. The copy was the only place they were ever opened. Her Mac volume was disassembled and put back together without issue. The tree was rebuilt exactly as it had existed prior to this episode. Files were verified as functional by being opened, rather than by merely being counted. Counting would have provided little insight.
What went home.
Almost everything is back now. The tree was sent home on new media, folder for folder. Every single file was opened here before it went. Only a very small portion didn’t make it back. Those were located in zones that consistently failed to provide a valid response throughout testing, and they’re specifically identified in the report with no associated percentage. The WD itself did not go back with the recovered data, since a drive that has once been unable to hand over what its own index points to has no business holding the second copy of anything.
Begin here if yours is doing the same thing.
Further portable-drive jobs, written up.
Yours doing something similar? Power it down first.
Published prices are fixed. Memory cards and USB sticks are £250 + VAT. Any stand-alone drive is £300 + VAT. Drive configurations containing multiple disks (RAID, NAS or server) start at £500 + VAT. First assessments are always complimentary. Thereafter, data recovery charges are also fixed in advance and in writing, so you'll always know how much you owe before paying any money. Shut it down, get a quote first (by phone or with the form), then send it in or drop it off at our Guildford intake laboratory, Monday to Friday, 9am to 5:30pm (no appointment needed). On most jobs you only pay if we recover your data.