re-adding a replacement into a pool of mirrors

[Randy Bush]

> It might be worth zeroing the whole disk with dd if=/dev/zero 
> of=/dev/da1s3 bs=64k, and then see if you can re-attach.

went single luser, zapped the drive, took a nap, then

    zpool attach tank da0s3 da1s3

worked.  so geom did have it!

thanks!

randy