I have a Retina MacBook Pro Mid-2014 with a 256GB drive, which is small for my needs so I need to use an external Hard Drive.
I'm using a WD 4TB My Passport where I store a lot of pictures and videos, I have my Photos.app library in the external drive and it is kind of slow. So I'm thinking about buying an external SSD to have a better experience working with my files. I think I would probably get a SanDisk 2TB Extreme Portable External SSD but if I can find a better similarly priced drive I could go for that one.
Considering my computer has USB 3.0, Would this be an improvement in speed?
From what I've understood it would be about a 3x speed improvement but I'm not sure and I don't want to buy a more expensive drive that does the same thing that the one I already have.
Best Answer
It should be an improvement in speed. USB 3.0 has a throughput of 5 Gb/s. Typical HDD's have a read speed of around 160 MB/s, which doesn't fully utilize USB 3.0's throughput. On the other hand, typical SATA-based SSD's have typical read speeds of 500 MB/s (which approaches but does not surpass USB 3.0's throughput). So, for most uses, you should see a speed increase.
There are NVMe SSD drives, for example, which offer much faster read/write speeds compared to older SATA-based drives (think thousands of MB/s). Such drives would be bottlenecked if used through externally USB 3.0. This shouldn't be a concern for you in this scenario, since the drive you listed doesn't fully occupy USB 3.0's speeds. Even if it did, you'll notice a speed increase since HDD's operate much slower than USB 3.0's speeds.
(For other readers considering using an NVMe drive externally, consider using a thunderbolt-based enclosure, such as this. There are also standalone external SSDs that use thunderbolt and offer faster speeds than what USB 3.0 would allow)
More importantly, SSD's excel at random read accesses. For example, if you try copying many small files from an HDD, you'll notice that read speed tanks (e.g., down to hundreds of KB or less) even though the HDD is technically capable of much faster transmission. This is because HDD's need seeking time to move their heads between accessing each file. Thus, the above read speeds are sustained speeds, where the device is reading data from one location. SSD's need negligible time between each file access, so you should expect pretty fast speeds even if your accessing many files at once. This distinction is very apparent when open a folder that contains a large number of files (similar to refreshing to your media library in your Photos app).
I did notice that your WD drive lists faster "maximum" read speeds than the SanDisk SSD. I suspect that you'd probably won't notice these speeds (either because it's wrong or because it only occurs in rare circumstances). You can try benchmarking your current drive to see if it is capable of those speeds. Most benchmarking software will also give you different results for sustained and random accesses. Again, note that your WD drive will only achieve those speeds when transferring single, large files.
The summary of this all is: yes, you should expect faster speeds if you buy the SSD you listed. The SATA-based SSD should be faster while not fully utilizing USB 3.0's maximum speeds. The SSD will also benefit you if your working with many different "small" files (like photos).
You'll notice less of a benefit if you are only storing big files (maybe your videos, depending on how large they are). If you are waiting a long time to refresh your library, an SSD will definitely help there (since this task requires accessing many different files).
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