Checkdisk on Production system - fixing issues without unmountingdrives

I have a prod system with several tera of SAN disk attached. The

filesystem was acting up and the drive has critical issues now on

about 30% of the data, and we need to run a checkdisk to repair the

issue. The downside is that it'll take over 3 days of downtime to run

checkdisk due to the size of data, and the fact that checkdisk

requires that we unmount the drives so users are all ofline for that

time.

Since there's no 3 day weekends coming up soon does anyone have an

idea to fix the drives without unmounting them?