Not even "ballpark", although I suppose I should try for that. Right
now, just a minimal sanity check, write 32 MiB, flush the port, make
sure the free-space is smaller than it was before I started writing to
/tmp. And John's EC2 example of 10GiB for all of / including /tmp
hopefully wouldn't fail with this "small" a write. But if so, it
could probably be moderately safely if smaller.
I'm no expert, but is there any way to cons up a temporary file system from the command line, then write to that? That way, you could guarantee that no one else was writing to it. For example, a RAM disk?