Scrubbing the entire raid volume is significantly different from scrubbing every piece of data as it gets written/read. First, in between your monthly/weekly s

Scrubbing the entire raid volume is significantly different from scrubbing every piece of data as it gets written/read. First, in between your monthly/weekly scrubs your disks/controllers will be silently corrupting data, possibly generating errors on multiple devices resulting in data loss depending on raid type. ZFS detects corruption much more quickly. Second, your traditional raid recovery is to rewriting the entire device to fix a single block. Let's say you're using RAID5 and you're rewriting parity. You get another block error. Oops, now you've lost everything. Since disks have an uncorrectible block error rate of 1 in 10^15 bits, you only need a moderately sized array to almost guarantee data loss. ZFS rewrites corrupt data on the fly.