I just finished installing Arch and my 3TB GPT drive (this is not my boot drive) is not showing in arch. I initialised it as GPT on my windows 7 machine and that machine is still able to read from that drive. Does it have to do with UEFI? My mobo is UEFI and my windows installation is installed as EFI. I wasn't sure how to do EFI on arch and some threads mentioned arch would automatically recognise the UEFI BIOS (I am not too sure about the relation between UEFI and OS installation, so please be gentle if my assumptions are wrong).
Arch not recognising GPT drive
arch linux;gpt
I have no idea why the partition isn't showing up on your Arch desktop (IMO GUIs are strange and unreliable and often have annoying hard-coded assumptions1) but if the partition is visible to the operating system, e.g. with sudo fdisk -l or sudo blkid or sudo lsblk then you can manually mount the partition anywhere you like.  For example:sudo mkdir -p /windows-datasudo mount -t ntfs -o ro /dev/sda2 /windows-dataYou can, as always, tweak the exact mount options (e.g. for uid, gid, perms) to suit your needs.You can also cause the partition to be auto-mounted by adding a line to /etc/fstab, something like:/dev/sda2 /windows-data ntfs uid=1000,gid=1000,noatime,allow_other 0   2(that's all on one line, not two lines)1 If I had to guess, I'd say that the Arch desktop knows what an HPFS/NTFS/exFAT partition is and will display it but doesn't know what a Microsoft basic data is, so ignores it.