I'm running out of macbook pro space (currently 120Gb) and would like to boost it to the 480Gb mark.

If I go and buy 360Gb on an external USB 3 SSD device, is it reasonable to expect that to perform somewhere near as well as replacing my existing internal 120Gb SSD drive with a new 480Gb drive?

I don't intend to use this space for a backup so it needs to function pretty close to my existing SSD drive in terms of speed. I've been finding pretty conflicting information from the research I've done so far, but would really like to believe this...

"SSD easily go up to 6 gb/s while usb 3.0 is still at around 4 gbps on modern systems. To me the HDD + USB 3.0 or esata setup is probably the most cost effective setup - the hard drive would more likely be the bottleneck, and would still blow away a USB2.0 setup where the USB connection is the bottleneck."

(from Internal drives vs USB-3 with external SSD or eSata with External SSD)

Thanks for any thoughts.

  • You should most likely expect an external drive to perform worse than an internal drive, unless everything you are working with is very small in size to the point that read/write time is negligible. – Musselman Aug 8 '16 at 17:03
  • And even then you add latency. Escept for eSATA, external SAS or maybe thunderbolt. – Hennes Aug 8 '16 at 17:41

If I go and buy 360GB on an external USB 3 SSD device, is it reasonable to expect that to perform somewhere near as well as replacing my existing internal 120GB SSD drive with a new 480GB drive?

No. And it depends.

Just using USB 3 will not make it almost just as fast. You can get close by using USB3 with an enclosure which supports the USB attached SCSI protocol, but you will still add some overhead by involving the USB stack. Using raw access via PCI-e (M2.NVME SSDs) or SATA based SSD will always be faster.

The questions you might want to ask yourself though are:

  1. Will it be fast enough for me?
  2. Do I mind carrying around a second device?

My own choice would be a single larger SSD in any laptop. And if I used that to store movies, music, iso's or other huge files I would consider an affordable classic HDD (aka rotating rust) for that since random access is not important to them and classic drives work perfectly well with that acces pattern.

But those are personal choices. And I do my gaming on a desktop, so I do not need much space for the OS. If you game on the macbook then a larger internal SSD certainly becomes more interesting.


Specifically what kind of Mac-Pro do you have? Hennes is pretty much on point already. If you want to use the Pros of an SSD, you could potentially do so using USB3.0 with little to no restrictions. However, just as Hennes I seriously doubt your need for an extra SSD for your usecase. Even if you needed one, there are better ways to update your SSD storage instead on an external SSD. You could replace your internal SSD for example (possible even for macs), or install an extra SSD/HDD in your optical-drive bay.

Another go around for your problem (expanding storage space), which I can only recommend if you don't constantly write new data on it, would be something like this:


It just uses a micro-sd card (to be bought seperately) as storage, which you can insert in the special adapter which almost completely disappears in your laptop.

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