# I assumed that disk A is not mounted as the root (/) filesystem. If it is, just ignore lines with disk A./dev/diskA /var/www/ auto defaults 1 2
/dev/diskB /ver/www/upload auto defaults 1 2
# You can replace "auto" by the filesystem you have on that partition, but the above should work anyway.
Synblic link if disks A and B are mounted elsewhere:
ln -s /path/to/driveA_mountpoint /var/www/
ln -s /path/to/driveB_mountpoint /var/www/upload
# Note: /var/www and directory "upload" on driveA must not exist or this will fail.
Use the bind option of “mount” command:
mount -o bind /var/www/ /path/to/driveA_mountpoint
mount -o bind /var/www/upload /path/to/driveB_mountpoint