The CHKSUM errors for c4t0d0s0 was growing and then suddenly drops and has a decimal point (that there are a lot of errors is another story):
pool: mypool
state: ONLINE
status: One or more devices has experienced an unrecoverable error. An
attempt was made to correct the error. Applications are unaffected.
action: Determine if the device needs to be replaced, and clear the errors
using 'zpool clear' or replace the device with 'zpool replace'.
see: http://www.sun.com/msg/ZFS-8000-9P
scrub: scrub completed with 0 errors on Thu Jan 18 16:21:32 2007
config:
NAME STATE READ WRITE CKSUM
mypool ONLINE 0 0 0
mirror ONLINE 0 0 0
c0d0p3 ONLINE 0 0 0
c4t0d0s0 ONLINE 0 0 48.14
errors: No known data errors