How long does a disk-cache double-check last?

Yesterday I started a cache double-check.
After 14 hours, it was still crunching, the
disk cache at the moment was 15 gigs big,
distributed among 5 diskd-based dirs on different
HDDs.

CPU usage was very low, disk usage very high,
response by squid was very sluggish.

So.. how long should I expect it to run?
1 hour/gig seems a pretty big time...

-- 
	/kinkie