I am planning to upgrade the code from 9.4.6 to 10.2.4 HF7 on BIG-IP 3600 type C103. HD1.1 is the active boot partition on 9.4.6.

You can have volumes or partitions, but not both. Volumes are preferred, but if you want to keep 9.x installed, you have to use partitions. Essentially, "volumes" means LVM, which gives you more flexibility about resizing on-the-fly etc.

However, even if you use partitions, you probably can't use the partitions you already have, because the partitions created by the 9.x installer are too small for 10.x. So whatever you do, the first step will be to reformat the whole box and install 10.x. This will leave you with 10.x on HD1.1 and nothing on HD1.2.

If you chose partitions rather than volumes, you can then reinstall 9.x. However, when you do this, the 9.x installer will wipe out the GRUB entry needed for the 10.x "mosreboot" command. So you need to back this up, run the 9.x installer, then restore it, as documented in SOL11774.

It is possible to preserve the 9.x configuration during the upgrade. Personally, I like to get a clean 10.x install, take a backup, then restore the UCS file, because that way if there's a problem with the conversion, I have access to the clean state of 10.x. But you can run the conversion during the install, if that's your preference. I recently did a 9.4.6 to 10.2.4-HF7 upgrade on a pair of Big-IP 1600s and I had a problem where the UCS file didn't restore cleanly. I had to manually copy bigip_base.conf and then restore the rest of the UCS. I don't know if this is typical or just a problem in my environment.

Once booted to 10.2.4, you can use the software management feature of the web interface to perform the HF7 install. Copy the 10.2.4 and HF7 isos and md5s to /shared/images (I like to copy them with scp because I have a personal mistrust of web browser uploads, but again, that's just me). Then go to the web interface under System - Software Management - Hotfix List, click on the HF7 image, and choose a partition to install it in. (Note that you can't install overtop of the partition you're currently running from.)

Also, I think (but I'm not sure) that if you use v9.x-compatible partitions, then you only get HD1.1 and HD1.2 - I think you can only have three "slices" if you use volumes, which are incompatible with v9.x.