> Creating a hole is as easy as seeking beyond the end of a > file and scribbling something but maintaining its holeyness > by checking every write for a block of zeroes is quite > expensive.
It only needs to be done when writing to a hole, and for the small cost of a scan over the block, you get to avoid a few disk writes (more expensive). It's worth doing. Aux/disksim does this, specifically so that I can run tests on enormous files without needing the backing store. For example, that's how I checked tar's recently-added support for files > 4GB. Russ
