So, I'm thinking of upgrading my MBP (13' late 2011) with an internal SSD drive. I'm wondering if the increase in speed of read and write on the SSD internal drive, will increase peroformance and stability while reading data from other external HDD drives. I have a lot of data stored on external drives (iTunes, Photos, Audio sound libraries, ...) and wondering if I can expect significant improve on dealing with that external data on a daily basis. Thank you.
Honestly, it is a waste not to have an SSD as an internal drive in a MacBook (or any computer in general), you will understand it once you have one. Of course, the speed of your internal drive has absolutely nothing to do with that of external ones. The latter is only governed by the respective bus speed they are connected to.
Using internal SSD will make your system faster overall, including access to peripherals.
With that said, you might or might not notice the access speed change to external HDD.
That would depend how busy the resources was/is. System will still use the RAM as means to communicate between the disks. Assuming you have no bottleneck there, next possible slow down would be your connection to the external HDD.
If it is USB2 you get what you get there is no way around that and you might not see improvement. But if it is Thunderbolt or USB3 then you will see a improvement.
Here are some numbers:
USB2 max speed is 60 MB/sec (480 Mb/sec). Typically you will get less than that so around 30-40 MB/sec. With Thuderbolt or USB3 you will get 10 times the speed of USB2. If your goal is to increase the access sped to external drives, the solution is obvious.