Typo or not?

[Hannie Dumoleyn]

Before I file a bug, I would like to ask a native English speaker to 
have a look at this sentence:

When a disk/volume is considered "too full" depends on various factors, 
including the size of the disk and how fast you're filling it up. You 
might want to free up space if the disk/volume is more than 90% full.

I would think that "When" should be "Whether".

Hannie