I'm not saying that you wouldn't see any performance gain. 2TB on the outer track will be faster than 8TBs on the same 8TB disk, but I'm saying any gains will be lost due the dense nature of the drives.
A quick google search shows that there are marginal gains on the outer track vs the inner, but that is only on sequential workloads. For something like GitLab, the workloads would be anything but.
Ignore the part about where the partition is, then.
1. If I look at 2TB vs. 8TB HGST drives, their seek times are 8ms and 9ms respectively. But if you're only using a quarter of the 8TB drive, the drive arm needs to move less than a quarter as much. Won't that save at least 1ms?
2. The 8TB drive has a lot more data per inch, and it's spinning at the same speed. Once a read or write begins, it's going to finish a lot faster.
A quick google search shows that there are marginal gains on the outer track vs the inner, but that is only on sequential workloads. For something like GitLab, the workloads would be anything but.
http://superuser.com/questions/643013/are-partitions-to-the-...
https://www.pythian.com/blog/hard-drive-inner-or-outer/