It varies.
The “bootable flash drive” we’re talking about here goes by several different names: emergency disk, rescue disk, recovery disk, and perhaps others. It’s the drive you would boot your machine from in order to perform a full restore of an image backup.
There are several approaches as to how often you should create one, but I’ll give you one clue as to my strategy.
I don’t have even one.
Yet.
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Updating rescue media
You don’t need to make new copies of rescue media regularly. Most backup programs let you create it on demand on another computer when needed. If you only have one machine or use old software, keep a copy handy. Update it during major software changes.
Just-in-time rescue media
For the vast majority of backup programs, as long as you have another machine around, you can create the rescue media at the moment you need it. You don’t have to have one lying around, and you don’t have to worry if the one you have is the current version or not. Just run the backup software on a different machine1 and create the rescue media right there and then.
Then you can take it to the other machine, boot from it, and restore the image.
In most cases, it doesn’t even matter if you’re using a free or paid version of the same software; the rescue media is often the same, or it’s at least capable of performing the restore you need when you need it.
As I said, this is what I do.
Having rescue media on hand
What I’ve described above applies to most backup software packages and to most situations. There are cases, though, where you might want to make a copy of rescue media to keep on hand.
- You have one and only one machine. You won’t have a computer available to create a rescue disk if the one machine you have isn’t working.
- The backup software you’re using is very old (but still meets your needs). It’s rare but possible that newer versions of the same tool might not support the older format created by the version you’re using.
In cases like these, I would make rescue media when installing the backup software for the first time. If you’re already past that, make it as soon as you think about it.
Then save it somewhere you can easily find it if and when you need it.
Updating rescue media
There’s no hard-and-fast rule for updating rescue media either, other than you do not need to make new rescue media every time you back up.
I would create new rescue media under two circumstances.
- Your backup software goes through a major version update. Macrium’s update from 8 to X is a great example: they changed the backup format, and newer backups will not be readable by older rescue media.
- You’re advised by the release notes to do so. Sometimes, updates to the backup software include updates to the rescue media they create, so a new copy might be called for.
But that’s about it. You don’t need to spend a lot of time re-creating rescue media.
Do this
I recommend the just-in-time method, particularly if you have two or more computers. It might even be something you can rely on if you have a friend whose computer you can use at the time.
Otherwise, keep a copy, but don’t worry too much about re-creating it often.
And above all: back up. 
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Podcast audio
Footnotes & References
1: Or the current one, if it’s still running.
As long as the update isn’t a new version number, it’s almost certain that the file format won’t change. You can try it out. Run the recovery from the Flash drive and see if you can copy files from it.
I create the rescue disc when I install a new version. That way, I can just pop in the rescue disc to restore my system. If I have to create a rescue disk, it’s not a big deal for me because I have 3 Windows computers. If you have only one machine, it requires finding a friend (or at work) who can let you create a rescue disk on their machine. This can take a lot of time.
Bottom line, why not make a copy when you install the backup program. At the very least, it can save a little time. At best, it can save you lot of time.
I gave up special rescue media and these days use external SSDs with a bootable clone of the Windows installation. DiskGenius does do this fro free but there are other dedicated cloning programmes as Hasleo’s WinToUSB. The only PC where DiskGenius did not work was my MacBook with a Windows Bootcamp installation.
Such a “rescue medium” give you the luxury, that you can use all the tools that you are used too. And if your PC has a hardware failure you can simply boot your copy Windows from any other Windows machine, drivers these days are usually no problem anymore.
The only classical rescue medium I can recommend is a bootable USB device with Macrium Reflect 8 free. It has a built in tool for a hassle free repair for the boot sector that very often is corrupted after a restore of a backup of Windows. I have used it dozens of times.
Macrium Reflect no longer offers a free version. You can get the last free version form sites like MajorGeeks. It’s from Dec 2023, but it still should work.
If somebody has more than one computer, lets say one is very old and runs on Windows Vista, and another is modern and runs on Windows 10, can rescue disk created on the old/Vista machine be okay to run on the modern/Windows10 machine?
As long as the backup software itself can be installed on the older machine, yes.
I have a desktop and two laptop PCs. I use Macrium Reflect free from Older Geeks as my primary image backup software. I have a copy on my desktop PC and on both of my laptops. I created the Macrium Reflect Rescue ISO image and moved it to my Ventoy disk. I also keep a copy on an external drive along with other important software/files. Since Macrium has stopped offering the free version, and I will no longer receive updates to it, I only need to keep the ISO image I’ve created. It should continue to work as long as Macrium Reflect Free does on my computers. I’ve tested the rescue image, and it reads the backup image files, allowing me to access individual files. Note that I have Macrium Reflect verify image files when they’re created, and being able to access their content using the rescue ISO system gives me the confidence that I’ll be able to restore my system if the need should ever arise.
If I’m missing anything, please reply, telling me what I’ve missed,
Ernie