One of the obvious choices to avoid this problem its just to use the suspend or the hibernate function of your computer, which indeed works great. Sadly, it only works as long as you don't want to pause the process, and of course wouldn't prevent you from losing it to power loss or to a system failure. Losing 3 days of computing in a 12 core cpu hurts, i can tell you first hand. 

Thats where checkpoints come into play.  Checkpoints are implemented in basically any class of Virtualized environment, From VirtualBox, vmware and Qemu, to any console emulator. Consider it as the suspend mode of your computer, but instead of thrown away, they get stored, usually compressed. 

Because VirtualBox its the most popular environment, i rather not bother with other configurations. Although some people may get an advantage from using Qemu. 

In many computers the virtualization extensions are disabled by default. I believe its for security reasons, no antivirus will catch a monero miner in its own virtualized system. So make sure that they are activated first

Setting it up it's easy, just get BOINCOS : https://delta1512.github.io/BOINCOS/ 

Set up a hard drive, i recommend a static hard drive of at least 16 GiB , but a dynamic one shouldn't hurt. 

you may set it up to use as many CPUs as you have, or less. I recommend assigning it 200MB for every thread added. 

This comes with two clear downsides, the ram use its now static, and checkpoints must be manually recorded. Unfortunately there its no autocheckpoint function. 

If you are in Linux (or OSX or FreeBSD) , this script will surely help :

https://pastebin.com/eFg0f6au

It starts the VM, with no gui, records it status every 1 hour, configurable. 

You will probably want to make a systemd unit file for it : 

https://pastebin.com/URYwTeNe

And some instructions on how to use it : 

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/sect-managing_services_with_systemd-unit_files

And i believe we are done. O, and btw, there its a slight performance hit, but with an hour of computing youve saved using it, it would have had paid off. 

https://upload.wikimedia.org/wikipedia/commons/d/d5/Virtualbox_logo.png