I have three SCSI disks that I would like to use with Slackware. I have one 18GB drive that I just installed Slackware on. I also have two smaller drives that I would like to add on to be extra space. How would I go about doing this?

Edit /etc/fstab, and create the filesystem mount points.

I just added a primary partition on the extra disk, then added it to fstab with a mount point being / and it doesn't appear to have worked when I do a df -h to see my diskspace available. Should I have made it an extended partition instead of a primary?? What is the difference between an extended and primary partition anyways?

the usual line is that you should have no more that 4 primary partions. Windows and dos install only on primary partitions. Extended partitions are made on primary partion( on my last primary) to allow more than for 4 partions. Linux can install to any of these as well as to a primary partition. Many install guides discuss this matter extensively. See LinuxQuestions.org>LinuxAnswers>Hardware>A short guide on partitioning a hd for linux and one on scsi raid.
someone using scsi disks can help with them or use google-slacware on scsi disks for example.

I changed it to where it now mounts the /dev/sdb1 on /home and it works fine. How can I just get the new drive to be an extension of / so that I can just use them together, basically as just one drive?

Hmm.. I don't think you can split the root file system in the way you are proposing. You can place specific pieces of it on different partitions and different disks (i.e. /home on one disk, /tmp on another etc., but not / after you have done the initial installation). The reason being is that I believe / needs a single mount point. I don't think you can get any mount point to stretch over two partitions... unless you're doing some type of raid set up, but I have no experience with that... hence my limited knowledge on the subject.

What I would do if I were you is pick sections of root filesystem you'd like to move, (i.e. again, /home, /tmp, etc.) and create new mount points for those in your fstab file. (I wouldn't know how to go about deleting the originals, and personally I'd backup my home data, xorg.conf file, kernel, etc. and do a fresh install making the new mount points.)

What you're talking about is similar to RAID striping, so you might want to try searching for information on that topic.

If you decide on the fresh install route I found a link that might help make your backup migration easier... I haven't read the whole thing though:

http://www.faqs.org/docs/Linux-mini/...k-Upgrade.html

Excellent. That's exactly what I needed to know. Thanks.