[pve-devel] [PATCH 1/4] RFC: Efficient VM backup for qemu

[Dietmar Maurer]

> > Do you keep some blocks maps in memory ? (if yes, what is the memory
> > usage with big volume?)
> 
> Yes, we use a bitmap, one bit for one cluster (cluster size = 65536 bytes)
> 
> 1 TB ==> 16MB bitmap
> 
> 2^40/2^16 = 2^(40-16) = 2^24

Oh, just noticed that this is the number of bits (not bytes), so you
need to divide above result by 8:

1 TB ==> 2MB bitmap

I guess that is small enough.