Sparse file issues with docker

[pspicer-craniumai]

When using Fuji on a system with docker installed, the sparse file for Docker.raw may appear to be essentially the size of the disk. During acquisition, it appears it is read/copied as its full size, as i had it sitting on Docker.raw for a couple hours after which it ran out of space and the rest of the acquisition failed. Is there a configuration or way to get it to recognize only the used space rather than allocated space?

[pspicer-craniumai]

This is when using ditto acquisition from recovery, by the way

[Lazza]

Ditto should preserve the compression for source files, as stated in the man page:

     --preserveHFSCompression
                   When copying files to an HFS+ or APFS volume that supports filesystem compression, ditto will preserve the compression of any source files
                   that were using filesystem compression.  This flag is only supported on Mac OS X 10.6 or later.  --preserveHFSCompression is the default.

There is a flag to force compression for all appropriate files (--hfsCompression) but it is unclear whether this would have any negative effects on speed or on the final image.

Please note that this is different from using global compression for the disk image itself. The temporary read-write sparseimage cannot be compressed, it is only sparse. The final DMG is compressed.