iMac 27 inch 2019 external ssd or pay Apple exhorbitant fee for internal ssd

I am close to buying a new iMac 27 inch 2019 with the i9 CPU. I would like to have a 2TB internal SSD but I can purchace a blazing fast external drive for much less money. OWC has a 2 TB SSD for $500 (OWC Pro EX) that gets up to 2500 MB/s (doesn’t say read or write). Would this be much slower than the internal SSD?

The ultimate read/write speed depends upon the connection you can use for the external SSD.

USB will be slower than Thunderbolt even if the drive itself is fast.

An internal drive on the SATA bus will be much faster than an external drive. If the drive will be mainly used for archiving or backup, then an external will work just fine.

My suggestion would be to spec a larger SSD for your primary drive (OS, apps, frequently accessed docs or images) and external drives for archiving and back up. Keep in mind that SSD’s need free space (at east 10%, and preferably more) for optimizing. So be sure to get one larger than you think you will need.

Thanks Preston. I’m actually already doing your suggestion on my current set up. My boot drive is a 1 TB internal SSD, and I store my photos on external USB 3 connected spinning hard drives. After a photo trip I keep the photos on the internal drive until I am basically done editing the bunch, then move them to the external drives. Opening, closing, and saving photos on the external drives is noticeably slower. Even with an internal drive of 1 TB there are times when I wish I had more boot drive space, hence my desire for a 2 TB boot drive. Apple charges $1100 to upgrade the basic model to a 2 TB SSD, and the 2TB OWC drive I mention in my original post sells for $500. I would use it as my boot drive. Hence my question about would the external SSD drive be much slower.


I would not use an external drive for a boot drive. The performance would be sub-par because the USB3, even though it’s fast, cannot compare to an internal SATA bus for speed.

Question; Can you, or a competent tech install an aftermarket 2TB SATA SSD in the iMac? (I’m a PC guy, so don’t know if this is possible) If you can, you could buy a compatible SSD and then install it for less money than the factory upgrade.

Macs have a different internal environment that PCs. iMacs have not had a SATA bus for four or five years, they only use the much faster PCIe system to connect SSDs to the motherboard. Measured read write speeds by various internet geeks are all in the 2000/2500 range, which is a similar range for the OWC Thunderbolt 3 external SSD drive that I referenced above. What I am trying to find out is if there is any real world difference between the Mac supplied internal drive, or any of the fast Thunderbolt 3 available SSDs, since the external drives are much much cheaper and their theoretical speeds are similar.

I have pretty much the same Mac, and have two 12TB Thunderbolt 3 connected drives from G Drive. They are traditional spinning drives, and I edit 4K video without any slow downs, and work on 300+ Megapixel large format film sans with file sizes in the 6+GB range from those drives and they are very fast. SSDs are awesome, but a spinning drive on Thunderbolt 3 passes the test for me.