sorry forgot to mention i only own macs so i can't use putty. But here is what I've done.
I went back to the disk that was showing checksum errors and brought it offline
After that i wiped that disk with zeros to clear any data that was on it.
I then resilvered the wiped drive to bring it back into the mirror and turns out all the checksum errors disappeared and my volume status returned back to healthy instead of degraded. Not sure what caused it to degrade in the first place but wiping the drive and brining it back into the array seemed to do the trick.
Im not sure if this is the same as what you were asking me to do using putty but i went into my shell and did the same commands and came back with this...
Im assuming all is good now?
[root@freenas ~]# zpool status -v pool: HDD state: ONLINE scan: resilvered 620G in 4h13m with 0 errors on Tue Mar 18 01:16:51 2014 config: NAME STATE READ WRITE CKSUM HDD ONLINE 0 0 0 mirror-0 ONLINE 0 0 0 gptid/7fa5dc93-ad7c-11e3-b657-bc5ff4d30f58.eli ONLINE 0 0 0 gptid/14a0bcca-ae52-11e3-b924-bc5ff4d30f58.eli ONLINE 0 0 0 errors: No known data errors [root@freenas ~]# camcontrol devlist <WDC WD20EFRX-68EUZN0 80.00A80> at scbus0 target 0 lun 0 (ada0,pass0) <WDC WD20EFRX-68EUZN0 80.00A80> at scbus2 target 0 lun 0 (ada1,pass1) < USB Flash Memory PMAP> at scbus9 target 0 lun 0 (pass2,da0) [root@freenas ~]#