multiple threads/ cpus when checking files on different drives

[gloryglory]

at the moment, file checking due to crashes, etc are only done individually one at a time even if there are multiple cpus and drives available.

The checking operation can be vastly speeded up if multiple cpus are able to be used to check multiple files on multiple drives concurrently. One cpu per drive will mean much faster checking

[Firon]

It's not CPU limited. It's only I/O limited.

And we already made disk multithreaded in 3.3.