feature: optional pre-allocation

[onlyjob]

Pre-allocation may be useless

• When file system is exclusively used by one application
• On certain file systems

Please consider making pre-allocation optional.

Thanks.

[dylanetaft]

A quick commit review - I don't think they're preallocating primarily to reduce filesystem fragmentation. They're doing it to avoid inner-file fragmentation, internally the file is ordered - see line 364 https://github.com/alter3d/omdcct/commit/266d8499bf6499517e2a74d49fe33f81e3fb4b80

So when you go to read it, you're not seeking all over, the file becomes indexed. Not sure how the miner code handles reading the file. Would have to review to ensure it uses that indexed order to benefit.