To use the term “sparse file” to also refer to files with large continuous runs of zeros, created via a seek operation, is just confusing. Those are quite explicitly not sparse files, they’re just files, that happen to be full of zeros (all written to disk). “Sparse file” are quite explicitly the result of the optimisation to avoid writing pointless zeros when preallocating a large file that’s going to written into in an unordered manner.
Using the term “sparse files” to refer to both the “problem” and the “solution” is just unhelpful, and doesn’t align with the accepted meaning of the term.
Unfortunately for COW filesystems including zfs and btrfs fallocate doesn’t do anything useful for preallocation. You’re still going to get fragmentation. The two methods outlined are essentially equivalent.
Eh, agree to disagree.
> Unfortunately for COW filesystems including zfs and btrfs fallocate doesn’t do anything useful for preallocation.
Both ZFS and BtrFS have "nocow" modes that are probably more suitable to this type of use case. And other filesystems are widely used.
