Finding a Thunderbolt 3 SSD for iMac 27 2020 backup

I use a Crucial X9 2TB drive for TM backups on my 2020 27-inch iMac. That drive is a USB-C 3.2 Gen 2 (10 Mbps) rated drive (1050 MB/s) and it is plugged into one of my TB3 ports. Backups happen so quickly that there is rarely time to see the menu bar icon change.

OWC rates their TB5 Envoy Ultra at 6000 Mbps when connected to a TB5 port and 2800 Mbps when connected to a Mac TB3 port. It is not a cheap device and wasting all that potential bandwidth and expense is not practical. Although I do have an Envoy Ultra, it is connected to the TB5 port on my M4 Mac Mini Pro exclusively for Parallel's Desktop virtual machine guests (which do boot quickly).

I have the same iMac. You do not want a TB4 or TB5 drive of latest design as they will run slow on your iMac. You need an earlier model of TB enclosure using any NVME drive. I use an Acasis enclosure with a WD Black NVME drive. One like this:https://www.amazon.com/dp/B0BB74BQVN?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_11&th=1

The latest TB enclosures (supporting fast TB4-5 ports) use a different chip which does not play nice with the older TB3 Macs.

There are lots of Thunderbolt 3 SSDs if you look for them.

However, I agree with VikingOSX that you do not need a Thunderbolt 3 SSD for backup, especially on a Mac with a 256 GB startup drive. I have a Mac Studio with a 512 GB SSD, and one of the drives that I use for backups is a 1 TB Crucial X9 Pro (reformatted to APFS). I use Carbon Copy Cloner, and do incremental backups, and those take very little time, even though the SSD is "only" a USB 3.1 Gen 2 SSD.

jmnorlin wrote:

The speed of Thunderbolt 3 is 40 GB/s according to the spec.

Can you help me find a SSD which can be connected to Thunderbolt 3? Can a USB-C SSD be connected to the Thunderbolt 3 and at what speed?

The maximum speed of Thunderbolt 3 is 40Gb/s ..... notice the lower case "b" which is very critical since that 40Gb/s equates to about 5GB/s (notice the uppercase "B" in the 5GB/s).

FYI, be careful about reading too much into the speeds listed for any device. Many times the manufacturer of an external drive will be highlighting the maximum theoretical speed of the protocol instead of the product's real world transfer rates. You must be very careful reading the numbers for the actual transfer rate of the product versus the port protocol.

The other issue with worrying about all these numbers is that even the 40Gb/s theoretical maximum of each Thunderbolt 3 port has some caveats as well on these Macs. Many of the Apple Thunderbolt 3 ports share an internal bus so that 40Gb/s maximum may be shared between two of those Thunderbolt3 ports. Since there are only two ports on some Macs. See the following article for some specific details:

https://macperformanceguide.com/blog/2019/20190128_1352-understanding-Thunderbolt3-bandwidth.html

As others have mentioned you probably have no need for a Thunderbolt3 backup drive for just a small 250GB internal SSD.

jmnorlin wrote:

The Thunderbolt compability information on the OWC pages is excellent like their products. The price level is too high for me.

I understand. That's the reason for pointing out a SSD is overkill for Time Machine. Even more so when you realize it's a better idea to buy two or more HDDs since any device can fail at any time. Multiple redundant SSDs get expensive fast.

40 GB/s is a theoretical maximum that means very little in practice. You won't get anywhere close to that with any SSDs. The good thing is that you don't have to, not for Time Machine anyway.

https://eshop.macsales.com/shop/external-storage#thunderbolt-drives

Can a USB-C SSD be connected to the Thunderbolt 3 and at what speed?

40 GB/s

The SSD will be used for backup.

Actual data transfer throughput rate is nearly irrelevant for Time Machine. Time Machine backups to USB hard disk drives will be nearly as fast. Hard disks generally fail in a predictable manner, and are more disposable than SSDs.

Yes.

For a comprehensive answer that should put your concerns to rest, read https://eshop.macsales.com/blog/96867-the-simple-guide-to-thunderbolt-forwards-and-backwards-compatibility/.

FYI I am not affiliated with OWC or have any interest in recommending them, but I have used their products for literally decades and have no complaints. There are other vendors, so use that free information to your advantage.

jmnorlin wrote:

Are SSDs with Thunderbolt 4 or 5 backwards compatible with Thunderbolt 3 and have the same connection?

In most cases, yes.

According to an article on the OWC site, there is a special case when you are using an old computer that has an old-style Thunderbolt 1 or 2 host port. Thunderbolt 4 and 5 devices, like drives and docks, are only backwards compatible with Thunderbolt host ports that have USB-C connectors. So no connecting them to ancient Macs that have Thunderbolt 1 and 2 ports – even with the aid of the Apple adapter.

OWC Rocket Yard Blog – The Simple Guide to Thunderbolt Forwards and Backwards Compatibility

Another article discusses subtle differences between Thunderbolt 3 and 4.

OWC Blog – What’s the Difference Between Thunderbolt 3 and Thunderbolt 4?

John Galt wrote:

Can a USB-C SSD be connected to the Thunderbolt 3 and at what speed?

40 GB/s

FYI, I think the OP was asking about USB based transfer rates of those USB-C ports here since the OP had already mentioned the Thunderbolt 3 speeds correctly.

With a 2020 iMac, the USB3 maximum transfer rate using a USB-C port is just 10Gb/s (aka about 1GB/s) according to the following Apple article and as @VikingOSX mentioned:

iMac (Retina 5K, 27-inch, 2020) - Technical Specifications - Apple Support