Too slow with VMDK

[eduardobcastro]

I've been using a Debian VM under Windows host for a year and it was working fine until I converted one of my 2TB VDI disk where my home director is mounted to a dynamically allocated 2GB VMDK splitted (more than 1000 files).
Now it takes 2 minutes with the message Starting Virtual Machine. The guest system is slower also. And it takes 1 minute to force stop the VM without ACPI.
Tried to enable host IO cache without success.
I changed to a splitted volume because I want to back up faster. Any fix or alternative?

[mpack]

Why would you expect 1000+ 2GB files get backed up faster than one 2000GB file? That does not match my experience.

And are you sure the format is dynamic? Because if it was fixed then copying 1000+ 2GB files is certainly going to take a while.

To undo this change you have to do the same thing that you did to create it, i.e. clone the disk and (I would suggest) choose the dynamic VDI format for output. Changing the VDI disk to a less extreme size would be useful too. Most of my VMs have a 32GB drive capacity. I have one Win10 VM with 256GB. You would need a third party tool to accomplish the move and shrink of disk partitions.

As for the backup medium, a smaller virtual drive will fix the speed problem. I also suggest you choose a filesystem for the backup medium that doesn't require you to split large files.

[eduardobcastro]

Why would you expect 1000+ 2GB files get backed up faster than one 2000GB file?

I do differential backups. Not all 2GB will be modified when I do my backups but with a single big file just 1 bit changed makes me to copy the full file.

[scottgus1]

I do differential backups...with a single big file just 1 bit changed makes me to copy the full file

FWIW when I do a Macrium Reflect Free differential backup of my host, only the changed disk sectors get backed up, not the entire several dozens of unchanged GB. Maybe your backup software can do the same?

[fth0]

I would simply do the backups from inside the VM.

[socratis]

Have you considered the runtime cost of having 2000 files open just to read something? From multiple files potentially? Hence the slowdown?

[eduardobcastro]

I thought VirtualBox would use the files only when needed. I'll consider changing my backup software or doing backups from inside the VM.