The maxim “first, do no harm” is a great first rule for data recovery, and is at the heart of our whole approach. If you’ve lost data, it’s only natural to panic, but the safest thing to do is stop and get advice. It’s usually best to switch everything off, but there are rare times where you wouldn’t want to do that either.
When you should switch off a failed disk
If the drive has failed completely and you can’t access the data, definitely switch it off. If the disk is clicking, or making strange noises, switch it off. Certain types of hardware failure will get worse if you leave the drive powered on. If the heads have been damaged, they could scrape all the magnetic storage coating from the disk. When the heads are stuck on the disk, they can be wrenched off and take a chunk of disk with them.
If you’ve accidentally deleted some files from a disk, switch it off. You might not realise but as your computer sits there idle, there are all sorts of processes, downloads, updates and other background tasks that will be writing to your disk. Also a system task could attempt to repair the disk, or reset the computer and overwrite your files. All of these issues are avoided if the device is turned off. Your computer will happily reuse the space where your deleted files are, so once files are deleted it’s crucial to stop the computer accessing the disk. Once data is overwritten it really is gone for good despite what anyone tells you.
If you have a cloud service setup, you should download the data using another computer & disk. Make sure you check the downloaded data thoroughly before writing it back to your original disk. If you write the cloud data straight back to your computer, you’ve lost any chance of getting more data back if there’s something missing.
When you shouldn’t switch off a failed disk
If the data shows up at some point, copy it straight off. Hard drives are complicated machines, but sometimes the stars align and give you one last chance to access the files. Make sure you have enough free space on another disk, and make a copy of your files while you still can. There is a chance that if you power the disk down it might never show up again. Don’t waste that chance!
⚠️ If you start copying files and the speed goes down, while the time remaining goes up, you should stop and get advice. The hard drive could thrash itself to pieces trying to read the files and make recovery much more difficult. You don’t want to leave the disk unattended during this process, as it could fail and need to be switched off.