How to recover data from damaged Mac or external drive

It’s all very well telling people to back up. But human nature means that searching for backup advice is something that usually happens after the worst has already happened. Hopefully, you’ll be able to fix the damaged drive and get your data back by following our advice, but we will also cover what you need to know about crashing without a backup and how to recover data from damaged hard disk or an external drive.

This guide is also relevant if you have accidentally deleted a file. Deleted files can be retrieved too, but only if they haven’t been overwritten. Once the part of the disk with the data is overwritten, nothing can get it back.

If your drive isn’t a hard disk but an SSD (Solid State Drive) you may find the problem is more serious. SSDs are fundamentally different from HDDs, and although they seem to act the same, fixing them is a whole different matter, and the chances of recovery are far worse, however, we will examin your options below. 

This is part of a series of articles about backing up your Mac, read more here:

• How to back up your Mac
• Best cloud storage services
• Best backup software for Mac

Repair the failed Mac hard disk or SSD

If you are very lucky your hard drive (or SSD) isn’t beyond repair and you will be able to fix the problem yourself and therefore get access to your files.

If your drive is having problems and you become aware of this before the machine crashes, or if you manage to get it up and running again (or in the case of an external drive your Mac is able to detect it), the first thing to do is launch Disk Utility.

1. Open Disk Utility – You’ll find this in the Utilities folder, inside your Apps folder or by searching for it using Spotlight Search. (Press Command+Space to trigger this).
2. Click on the disk you are concerned about from the list on the left, and then click First Aid.
3. You will see a message indicating that First Aid will check the volume for errors. It will then repair the volume if necessary. 
4. You will see a warning that First Aid needs to temporatily lock the boot volume. This means that while First Aid is running apps won’t be responsive. The process probably won’t take long.
5. If during the process Disk Utility detects any issues and it’s easily fixed, then it should be resolved quickly.

We have a complete guide to using Disk Utility here.

Note that Apple updated Disk Utility in El Capitan and the options and capabilities have changed quite a bit since then. If you are using Yosemite or an even older version of Mac OS X, then you will see different options here, such as Repair Disk and the option to Repair Permissions…

Back in the day it would have also been advised that you should fix Disk Permissions, but Apple removed the ability to repair permissions in Sierra, probably because meddling with permissions can cause all sorts of issues.

If you are able to fix the hard drive or SSD in your Mac (or a external drive) using Disk Utility you will hopefully be able to recover your files. We suggest you back up your Mac at this point before running the risk of the disk failing again.

However, you may not be so lucky. Here’s what to do if your Mac won’t switch on again.

Restart in Recovery

It’s become something of a cliché, but turning it off and on again, is often a good way to reset any gremlins in your system. So it’s often the first bit of advice you’ll hear. However when dealing with dying disks, they may not survive the experience.

If you tried to restart and the drive didn’t survive the experience, you may find yourself in an even stickier situation. Now that modern Macs no longer ship with optical disk drives, you may not have an easy option to boot from another disk. Read: How to make a bootable OS X Yosemite install drive

However, as long as the drive failure isn’t too terminal, a restart in Recovery HD should be possible. This is actually a partition on the drive that contains a version of the macOS that you can boot from. Booting from this partition doesn’t do anything to the main drive, so there’s no need to worry about overwriting documents. We have a complete guide to using Recovery mode here.

In short, to enter Recovery you need to hold down Command+R while your Mac starts up. Keep holding those keys until you see either an Apple logo or a spinning globe.

If you manage to get in to Recovery mode, you should be able to run Disk Utility as described above, and potentially fix your disk so you can recover the data. 

One thing to bear in mind is that if you do manage to boot from Recovery, you’ll need another drive to recover files to. If Disk Utility manages to fix your drive enough to let you boot from it again, be very careful how you use it. You should plan to get an external drive plugged in as soon as you can, so that you can secure your data there.

If you have lost any data, it is very important to avoid using the drive, as anything that writes files to the drive, may be writing over your lost files. Which would render them unrecoverable.

So if you manage to resurrect your sickly drive, quit all your software, including email, to avoid overwriting any list files. Once you have an external drive, you can then use that as your boot drive, and recover any lost files to there.

If you have any disk management tools, like TechTool Pro, Disk Warrior or Drive Genius, you may able to try them out. They all claim to be more effective than Disk Utility, but how well they do is very dependent on whatever is at the root of the problem.  However, if you attempt to use these tools on an SSD, you’ll most likely find they aren’t quite so helpful. Unfortunatly, the way SSDs work is very different from HDDs that most traditional tools struggle to help at all.

What to do if there is no Recovery mode on the Mac

If you are using an old Mac running an OS older than Lion, then there will be no Recovery HD option. Lion has been around since 2011, so anything newer than that should have the Recovery HD partition available if the drive is showing any signs of life. If you have an older Mac, you will need to boot from an external drive either optical or HDD, that has OS X on it.

If your machine is running Lion or newer, and the Recovery HD isn’t showing, then it does suggest the drive problems are terminal. But you may as well try to boot from an external drive running OS X.

If you are able to get hold of either a DVD drive or an external drive with OS X already installed (we show you how to put macOS or Mac OS X on a bootable drive here), you’ll be able to boot from another drive.

Here’s how to boot from a drive containing macOS:

1. Restart your Mac and hold down the Alt/Option key.
2. When your machine gets to the point where it looks for an operating system to start from, it will give you the option to choose any suitable drive to start from.
3. Choose the external bootable drive.

If this works it puts you in a pretty good position to proceed, as you will no longer be booting from the faulty disk.

You can try running Disk Utility at this point and attempt to fix the faulty drive.

If that’s not possible then the problem may warrant using a data recovery app to retrieve any data you can, or, failing that a data recovery service such as Krollontrack, £99 might be able to do the job for you.

Using data recovery software

If you have managed to start your machine from either Recovery, or an external drive, the volume you are trying to recover still may not show up. Data recovery software can still work with that drive, so long as the OS can still talk to it. If the data is still on the drive, you still have a reasonable chance of recovering it.

There is one exception though, and that is if you were using an SSD. Because if the nature of SSDs, it is often impossible to retrieve data from them, no matter which tool you are using. This is because, unlike HDDs, SSDs would be very slow indeed if they had to save data to a block, or cell, that already has data on it. HDDs can merrily over write data over and over again. But SSDs must first erase that data to be able to quickly record new data. So SSDs have various strategies to manage this. OS X uses the TRIM system, which zeroes out the cells holding data is deleted, as part of is disk management. Other SSDs will always use a similar system, because if they needed erase and record at the same time, they would end up being slower than HDDs.

Put simply, when you delete data, SSDs actively reset their memory to be blank, while HDDs simply ignore any data in a block and only overwrite it if there is new data to store. We look at this in our SSD versus Hard Drive article.

The end result of that is that if you’re using an SSD and it fails, the chances of any data recovery software retrieving that data is slim to none. A sobering thought.

The annoying thing about data recovery software is that you only really use it if you have been caught without a backup. The developers have you at their mercy, and if you have lost precious data they could charge whatever they can get away with. But it is a highly competitive market too so the pricing structure has evolved at a sort of equilibrium. Some data recovery software if free (usually limited to a number of GB), and other options cost $99 or the UK £ equivalent of that.

The good news though, is that developers don’t want to you spend the $99 to then comeback and complain that it didn’t work. Thus a vast majority offer a free version that will scan your disk and see what is salvageable. You can then decide of the fragments of your dead drive are worth $99 to retrieve.

All work in a similar way. If the directory telling where files were originally stored is saveable, the rest is easy. But if that isn’t the case, the software will scan the data for familiar patterns that would denote a file type. Once they find as file type, there’s a good change that the following data will be the file. Highly fragmented hard drives might mean not all files can be retrieved, but given enough time, most will get there in the end.

It can be a time consuming process to piece the bits of files back together. But with patience, most files that haven’t been overwritten should in theory be saveable. If a hard drive is still spinning, and the head is still scanning, there is still hope. Sickly drives can take days to fully scan, and the higher capacity they are, the longer it will take. But if it’s your wedding photos, or perhaps your Bitcoin vault that is missing, you can afford to wait.

We have assessed the top Mac data recovery apps here.

Conclusion

If you don’t need data recovery right now, then do yourself a huge favour and make sure your backup strategy is up and running and fool proof. A little pain now will save you a world of hurt in the future. If you have already lost some data, then the process outlined here will help. But without wishing to pour salt in the wound, now would be a really good time to take a look at your back-up strategy. You can find a very comprehensive backup strategy here: How to back up your Mac.