Surface scan for Freebsd

[Jer]

Dear all

I have a feeling one of my disks is going south
Oct 28 11:28:40 computer /kernel: ad1: WRITE command timeout tag=0 serv=0 - 
resetting
Oct 28 11:28:40 computer /kernel: ata0: resetting devices .. done
Oct 28 11:28:55 computer /kernel: ad1: WRITE command timeout tag=0 serv=0 - 
resetting
Oct 28 11:28:55 computer /kernel: ata0: resetting devices .. done
Oct 28 11:29:06 computer /kernel: ad1: WRITE command timeout tag=0 serv=0 - 
resetting
Oct 28 11:29:06 computer /kernel: ata0: resetting devices .. done

how can i do a surgace scan of sorts so I can make them with badblock?

thanks
jer