Hacker News Reader

Additionally, while I don't know much about APFS, I don't think it would be beneficial to point the extracted app to blocks that are also part of the dmg file, i.e. some copying has to happen anyway.

View on HN

in a perfect theoretical filesystem, copy-on-write means copying is as cheap as moving a file, though uncompressing time makes sense.

Of course, but that works only if the files are already in the same partition. A dmg is a virtual image, even if it's stored in the same partition, once mounted it acts like another partition.

A perfect theoretical filesystem can still have subjective user configurable choices though right? Like case sensitivity, UTF normalization, checksum hash function, extra copies of data/metadata to store for redundancy/healing, etc (as well as compression/encryption). I think ZFS is a pretty strong real world example of a CoW FS, but you can still set a lot of different properties between sub-fs and then need to copy when you go between them to get the structural changes.

Disk images are supposed to function as if they're attached storage I think, and have different properties from what FS you're running on boot or your home folder (which themselves can be different, I run my home folder on my main Mac off a NAS via iSCSI). I'm not sure any underlying FS would avoid a copy operation there in general?

Reply on news.ycombinator.com