Storage space required by .img files

[ssh]

I have two cache pools. One of which is dedicated for my vms. This "vm" pool contains 1 device (a 250 GB SSD) is formatted as XFS.

There are currently 2 "vdisk1.img" files stored on that disk. They are listed as being 64.4 GB each.

Besides those, the only other thing that is on this SSD is the libvirt.img, which obtains 1.07 GB.

 

In my Unraid Main page, it shows that only 75.9 GB of the total 250 GB is used which is half of what I'd expect.

Is this a bug in calculating / showing the storage space used? Or do these .img files only take up the size according to how full they are?

 

If the latter is true, does that mean that I can in theory have more than 250GB of .img files stored on this disk? As long as they are not all full of course.

Edited March 20, 2021 by ssh

[John_M]

36 minutes ago, ssh said:

Or do these .img files only take up the size according to how full they are?

 

This. They are created as "sparse files". They grow as necessary, which will become a problem if you overcommit your storage and neglect to monitor its usage.

 

[JonathanM]

42 minutes ago, ssh said:

Or do these .img files only take up the size according to how full they are?

 

If the latter is true, does that mean that I can in theory have more than 250GB of .img files stored on this disk? As long as they are not all full of course.

This. vdisks are created sparse by default.

 

However, over-committing the available space can bite you if you don't manage it carefully.