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Power Outage Data Recovery Case Study: Gray Screen of Death

Gray Screen of Death

The question mark folder icon commonly seen on the "Gray Screen of Death".

The client in this data recovery case study came to us after a power outage. In the aftermath of the blackout, their iMac wouldn’t start up properly, showing only a gray screen and a folder with a question mark.

This was the “Gray Screen of Death”, Mac’s rough equivalent of Windows’ infamous Blue Screen of Death. The client tried to figure out whatever was preventing the computer from starting up properly and eventually discovered the culprit: their hard drive.

The hard drive held mountains of valuable data to the client: Quark Xpress documents, Quickbooks documents, and a treasure trove of photos. And when the client plugged the hard drive into another Mac to read and copy off its data, the entire drive showed up as blank.

The client sent their hard drive to Gillware Data Recovery, where our Mac data recovery experts could diagnose the drive and (hopefully) recover their data.


Power Outage Data Recovery Case Study: Dealing with a Gray Screen of Death
Drive Model: Western Digital WD3200AAJS-40VWA1
Drive Capacity: 320 GB
Operating/File System: Mac (HFS+)
Data Loss Situation: iMac had Gray Screen of Death after power outage; hard drive appeared blank when plugged into another computer
Type of Data Recovered: Quark Xpress projects, Quicken/Quickbooks, photos and documents
Binary Read: 99.6%
Gillware Data Recovery Case Rating: 9


Your Mac’s Gray Screen of Death isn’t necessarily caused by hard drive failure, like this customer’s (and a few others) was. Sometimes you can fix a Gray Screen of Death simply by rebooting your Mac (and of course, sometimes you can’t).

Diagnosing a Gray Screen of Death

Gray Screen of Death

The Gray Screen of Death is a kernel panic, which occurs when your operating system encounters an error so perplexing that it has no idea what to do. This can be caused by a hardware or driver issue with an internal component of your computer or something you have plugged into your computer. It can happen if something prevents the O/S from accessing critical system files, such as when key system files become corrupted.

To diagnose and fix a peripheral hardware issue: Try unplugging as many external devices as possible (printers, external hard drives, flash drives, USB hubs, etc.) except for your mouse and keyboard. This should resolve whatever driver issue is preventing your Mac from starting up properly.

To diagnose and fix an issue with corrupted or missing system files, you can boot into a diagnostic mode and run Disk Utility by holding Cmd+R, or booting from your O/S installation disk. After verifying your hard disk, you can run “Repair Disk” to address any logical problems with your hard drive if necessary, and run “Repair Disk Permissions” to fix corrupted or misplaced system files.

If nothing you try works, the problem may be due to a faulty motherboard in your Mac, or a hard drive failure. In the case of a failing motherboard, you can still remove your hard drive and copy data off of it onto another Mac, but you will need to rely on Apple computer repair experts to replace the motherboard and get your computer back up and running.

If your hard drive has failed, you won’t be able to pull any data off of it—you’ll have to leave that to the professionals. Read on to find out how our engineers salvaged this client’s data after their hard drive died.

iMac Hard Drive Data Recovery

Repairing a failed hard drive after a power outage can require a heads swap in our cleanroom.Our hard drive data recovery engineers found that this Western Digital hard drive had in fact suffered damage from the blackout. The read/write heads had crashed and become mangled, scratching the surfaces of the platters. After using one out of our vast collection of donor hard drives to replace the read/write heads, our engineers started salvaging data from the failed hard drive.

In a hard drive, data lives on both surfaces of the spinning disk platters. In cases of platter damage, often one of the surfaces of one platter will suffer more damage than the others. Platter scratches cause irreversible data loss, as the physical sectors holding data are scraped off of the surfaces of the platters.

Platter scratches also frequently complicate data recovery work. In this case, our engineers could pull data smoothly from all but one of the platter surfaces. The one surface that had suffered the most damage gave our engineers a much bumpier ride. While our engineers managed to successfully read 99.6% of the sectors on the platters, the majority of the remaining sectors that were too damaged to read lived on this particular platter surface.

Our engineers managed to fully recover 86.8% of the user-created files from the client’s failed hard drive, as well as partially recovering numerous others. Many of the partially-recovered files still worked, albeit with obvious gaps and holes where sectors of data were missing. Our engineers focused their efforts on recovering the client’s most important files, and were able to fully and successfully recover the vast majority of the client’s critical documents, projects, and photos. As a result, we ranked this power outage data recovery case a 9 on our ten-point scale.

How a Power Outage Can Kill Your Hard Drive

Your hard drive uses an array of complex, sensitive devices to store, read, and write data. Those devices—the hard disk platters and the read/write heads—are the most at risk when the hard drive loses power. Obviously, a sudden loss of power is not a situation with a 100% hard drive fatality rate. But when a power outage kills your hard drive, here’s what happens:

When you normally power down your computer, it sends shutoff signals to your hard drive and tells it to suspend its operations. The read/write heads pull away from the platters before the spinning platters come to a stop, and the drive safely powers down.

But when the hard drive unexpectedly loses power, it doesn’t receive these signals. The platters stop spinning (because the hard drive isn’t receiving any power to its spindle motor anymore). But the read/write heads don’t always finish pulling away from the platters before the spinning stops. The heads are normally held aloft by a cushion of air generated by the spinning of the platters. And the sudden disappearance of this cushion can cause the heads to crash onto the platter surfaces. This can result in damage to both the heads and platters. As a result, the hard drive can appear to be blank, or even start to click or beep when you power it on.

In this data recovery case, our client suffered a blackout that killed their drive and gave their computer a startup error. But there’s also a slim chance that this can also happen if you do a hard reboot (i.e. holding down the power button until your computer turns off, or pulling the plug on it).

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