His Toshiba external won't open, yet still hasn't disappeared. It "recently stopped mounting" to his laptop, and although it is Mac-formatted and he tried it on both his "personal and work Macbooks", he got the same results each time: "the laptops can read the hard drives in disk utility but they wont mount, so i cant open my files." When you have a drive that shows up in Disk Utility, yet will not mount on more than one Mac, there is a logical volume fault on that drive, not a dead drive: the hardware is being recognised and the volume can be seen, but the structural damage to the file system is severe enough that macOS is refusing to mount it, which is the recoverable end of the spectrum.
| Media | Toshiba StorE alu2 external hard drive, Mac-formatted — visible in Disk Utility on two different Macs but refusing to mount; the owner's files inaccessible. |
| Reported situation | Drive stopped mounting to the laptop · Mac-formatted · tried on both personal and work MacBooks · appears in Disk Utility on both but will not mount · files inaccessible · recovery cost queried. |
| Fault class | Filesystem structure corruption on a detected drive — the volume present but unmountable behind damaged structures, distinct from a hardware failure where the drive would not appear; drive health to be confirmed. |
| Equipment used | Drive imaged under a hardware write-blocker before any interpretation · drive health confirmed on PC-3000 UDMA, since it is detected and the fault appears logical · Mac-native APFS/HFS+ structures parsed from the image in R-Studio, backup copies of the volume structures located and rebuilt · signature carving for anything the damaged structures no longer reference · recovered files validated by rendering. |
Appearing in Disk Utility is the most encouraging aspect of this, and it rules out the worst cases. The fact that both Macs can see the disk in Disk Utility indicates that there is power to the device, there is communication from the device and it is detected; and therefore, the hardware and the basic electronic components within the drive are functioning properly. A drive that had failed completely (i.e., either mechanically or electronically) would not show up at all. Therefore, when you can see the drive in Disk Utility, yet you cannot mount its volume, then you have identified a much smaller problem with your drive: it is fine enough to be seen, but its volume will not open.
Reads-but-won't-mount means your file system cannot be parsed by macOS. For macOS to mount a volume it has to "read" the structures which define and describe the file system. If the defining or descriptive structures for the file system are broken (or have been broken) then the volume shows up in Disk Utility, because the disk and partition were able to be recognised as being there. But since macOS can't make sense of the file system, it won't allow you to mount it. The data area behind the broken structures is usually still good; the problem is with the few small records that tell the operating system how to show you the volume, not with the space holding the files.
The same behaviour on two Macs proves it to be the drive (not either of the computers). Since the identical visible-but-unmountable behaviour was obtained from each testing environment, a personal MacBook and a work MacBook, no single machine's configuration or software can be the cause. The fault travels with the drive across different hardware environments, which is exactly what a logical volume problem does, and that points the work at the drive (and its file system) as opposed to either of the Macs.
The move to resist is Disk Utility's repair and erase, which is the main hazard. When you're presented with a volume that will not mount, the choice macOS gives you is First Aid, and ultimately Erase. First Aid writes the fixes to the disk and if the structure of the volume is damaged, then it could further corrupt it, and when you select Erase on a volume with damaged structures, then you're going to lose the data that was still recoverable outright. So neither should ever be run on the original drive; leave the original as-is and recover from an image.
Recovery reads and reconstructs the structures of your data from a copy. The volume's structures contain backup duplicates which can be used to restore files with their names in an organised manner. When these structures are absent, signature carving will allow for recovery of file data directly, without regard to name or organisation. A combination of both, and then merging the two, provides the maximum from a drive that is fundamentally healthy but has failed logically (organised files where possible, carved files elsewhere).
The honest prognosis is very optimistic, with the drive's physical health confirmed first. If you have a detected drive that has a logical volume fault (which means a file system issue), your chances are generally very good for recovering from the problem. The reason we verify the drive's health at the outset is to eliminate the possibility of an underlying hardware fault developing behind the symptoms we see as logical problems. We confirm that the contents are recoverable prior to charging you anything, and we do everything on a write-blocked image of the data, therefore First Aid will not be allowed to exacerbate the issue.
A hardware write blocker was applied to the drive during imaging, prior to any software reading the drive's contents, and the health of the drive was confirmed using PC-3000 UDMA. Mac-native APFS/HFS+ structures were parsed from the image of the drive using R-Studio. Backup copies of the volume structures were identified and rebuilt. Signature-based file carving was used for anything that the damaged APFS/HFS+ structures no longer referenced. All recovered files were rendered as part of validation.
Once the detected hard disk had been imaged, we rebuilt all of the volume structures using their backup copies, then returned the files with their organisation intact. The diagnostic cost is free and will complete within two working days of the hard disk arriving. We provide you with a single, fixed written quote with VAT already included in it, and if we cannot bring your data back, there is no charge for our services. The decode: appearing in Disk Utility indicates that the drive is alive, and while it may be visible but unable to mount, this represents a damaged volume rather than a dead drive. Your files come back, rebuilt from the volume's own backup structures on an image, and First Aid never gets the chance to deepen the damage.
Do not use First Aid and never click erase: First Aid will write to a volume whose structures have already been damaged and may further damage or corrupt the information, while erase will completely destroy all of your information. If you see the disk showing up in Disk Utility then the disk is alive and recognised; therefore, visible but unmountable indicates a logical fault (and this would mean the data is still intact behind it) as opposed to physical. If you receive the same results on both of your Macs then this confirms that there is an issue with the hard drive rather than one of the computers. Please stop replugging it, and get a quote, and have it imaged so it can be recovered from the copy.
Our case files are written up from genuine enquiries our lab has handled for customers across Swansea and South Wales, anonymised to protect client confidentiality. Each one describes the diagnostic and recovery approach our engineers apply to that fault, using the equipment listed.
Diagnostic provided at no charge. Fixed quote. In most cases you only pay if we recover your data. Start now or call the freephone.