There have been many reports of problems with Thunderbolt 5 support in Apple’s latest MacBook Pro and Mac mini models with M4 Pro and Max chips. Among the more concerning have been poor performance when accessing SSDs through TB5 docks and hubs, and the inability to drive more than two 4K displays through those. This article looks at what has changed, and what can currently be achieved when accessing SSDs either directly or via TB5 docks or hubs.

When I last tested these, using a Mac mini M4 Pro and Sequoia 15.2, I found that speeds measured through a TB5 dock were generally at least as good as those through a TB4 hub, with three notable exceptions:

• Write speed from a TB5 port to a TB3 SSD through a TB5 dock fell to 0.42 GB/s, little more than 10% of that of a direct connection and similar to that expected from a SATA SSD operating over USB 3.2 Gen 2.
• Write speed from a TB5 port to a USB4 SSD through a TB5 dock fell to 2.3 GB/s, about 62% of that expected.
• Write speeds to a TB3 SSD through a TB5 dock occur at about half the expected speed, just as those through a TB4 hub.

Methods

Three Macs were used for testing:

• iMac Pro (Intel, T2 chip) with macOS 15.1.1, over a Thunderbolt 3 port without USB4 support.
• MacBook Pro (M3 Pro) with macOS 15.2, over a Thunderbolt 4/USB4 port.
• Mac mini (M4 Pro) with macOS 15.3, over a Thunderbolt 5 port.

The results for the first two are taken from my previous tests, and here used for comparison.

The dock used was the Kensington SD5000T5 Thunderbolt 5 Triple Docking Station, with a total of three downstream TB5 ports. I’m very grateful to Sven who has provided his results from an OWC TB5 hub to support those from the dock.

Other methods are the same as those described previously. The TB5 SSD tested is one of the three currently available or on pre-order from OWC, Sabrent and LaCie (no, I’m not going to tell you which, as I’m still in the process of reviewing it).

Single SSDs

Results obtained from measuring read and write speeds on a single SSD at a time are summarised in the table below. Those that are concerning are set in bold italics.

Performance of the TB5 SSD when connected direct or through the dock was highest of all, and around 150% of the speeds achieved by the next fastest, the USB4 SSD, and around 180-250% those of the TB3 SSD, the slowest. Direct connection of USB4 SSDs to the TB5 port in macOS 15.3 resulted in even faster speeds than a TB4/USB4 connection using 15.2. Thus, a TB5 port with 15.3 delivers best performance over all types of external SSD tested here.

Of the three exceptionally poor results seen previously:

• Write speed from a TB5 port to a TB3 SSD through a TB5 dock improved greatly from 0.42 GB/s to 1.6 GB/s, the same as in other Macs.
• Write speed from a TB5 port to a USB4 SSD through a TB5 dock improved from 2.3 GB/s to 3.8 GB/s, the same as when connected direct.
• Write speeds to a TB3 SSD through a TB5 dock remained at 1.6 GB/s, about half the expected speed, just as those through a TB4 hub.

This anomalous behaviour when writing to a TB3 SSD through a TB5 dock was also found by Sven in his tests on the OWC TB5 hub, and seems common to most if not all TB4 and TB5 docks and hubs. I haven’t seen any explanation as to why it occurs so widely.

Paired SSDs

Encouraged by these substantial improvements with Sequoia 15.3, I measured simultaneous read and write speeds to a pair of USB4 SSDs connected to the Kensington TB5 dock. Stibium has a GUI so can’t perform this in perfect synchrony. However, it reads or writes a total of 160 files in 53 GB during each of these tests, and outlying measurements are discounted using the following robust statistical techniques:

• a 20% trimmed mean, giving the 20th and 80th centiles;
• Theil-Sen regression;
• linear regression through all measured values, returning a rate and latency.

Measured transfer rates in each of the two USB4 SSDs are given in the table below.

The first row of results gives the two write speeds measured simultaneously when both the SSDs were writing, similarly the second gives the two read speeds for simultaneous reading, and the bottom line shows speeds when one SSD was writing and the other reading at the same time.

When both SSDs were transferring their data in the same direction, individual speeds were about 3.1 GB/s, but when the directions of transfer were mixed, with one reading and the other writing, their speeds were similar to a single USB4 SSD. Total transfer speed was thus about 6.2 GB/s when in the same direction, but 7.2 GB/s when in opposite directions.

Multiple displays

Many of those buying into TB5 are doing so early because of its promised support for multiple displays. I haven’t yet seen sufficient evidence to decide whether this has improved with Sequoia 15.3. However, OWC has qualified full display support of its TB5 hub as requiring “native Thunderbolt 5 display or other displays that support USB-C connections and DisplayPort 2.1”. One likely reason for multiple displays not achieving support expected, such as three 4K at 144 Hz, is that they don’t support DisplayPort 2.1.

Which macOS?

As the evidence here suggests, macOS 15.3 or later is required for full TB5 performance, and OWC now includes that in the specifications for its TB5 hub. It also states that TB3 support requires macOS 15, although USB4 should still be supported in macOS 14 Sonoma.

Recommendations

• TB5 SSDs are faster than USB4, which are faster than TB3, in almost every combination. The only exception to this is a USB4 SSD connected direct to a TB3 port, which is likely to be limited to 1.0 GB/s in both directions.
• When pricing allows, prefer purchasing a ready-made TB5 SSD. If it’s to be used with an Intel Mac, confirm that it there supports TB3.
• Self-assembly TB5 enclosures remain expensive at present, and a USB4 enclosure may then prove better value, provided that it won’t be used with an Intel Mac.
• Avoid writing to a TB3 SSD connected to a dock or hub, as its speed is likely to be limited to 1.6 GB/s.
• Ensure Macs with TB5 ports are updated to Sequoia 15.3 or later.
• Ensure Macs to be used with TB5 docks or hubs are updated to Sequoia 15 or later, or they may not fully support TB3.

As the first batches of Thunderbolt 5 SSDs are starting to ship, this is a good time to take stock of what we have seen so far. Here I include some current results obtained from testing one of these new products.

So far, products that have already been released or are well into pre-order include:

• OWC Envoy Ultra,
• LaCie Rugged SSD Pro 5,
• Sabrent Rocket XTRM5.

Starting prices for these are under $/€/£ 400 for 2 TB, making them a little more expensive than better USB4 or Thunderbolt 3 equivalents. I am very grateful to Jozef for telling me that Acasis are promising to ship a TB5-compatible empty enclosure imminently, although at $300 it doesn’t make self-assembly attractive yet. If you’re interested, he has included a link to the product page in his comment below.

Mac support

The only Macs that currently support TB5 are the latest MacBook Pro and Mac minis equipped with M4 Pro or Max chips. Although they’re claimed to support full-speed TB5 performance when running macOS Sequoia 15.0, problems have been reported in achieving that, at least with TB5 docks and hubs. If you intend using any TB5 peripheral, then you’d best start with 15.3, which has been reported as solving at least some of those problems. This may also explain some of the anomalies in SSD performance that have been claimed by a few early testers.

Other Apple silicon Macs should run TB5 SSDs in USB4 40 Gb/s mode, which should still be significantly faster than TB3. Intel Macs don’t support TB5 or USB4, though, so they’re most likely to fall back to run them as USB 3.2 Gen 2, at 1 GB/s, which would be a deep disappointment for the cost.

Benchmarks

Beware of claimed performance of TB5 SSDs by their manufacturers and in product reviews. Testing them isn’t as straightforward as with slower products.

For a start, quoted results are often taken from apps such as Blackmagic Disk Speed Test and AmorphousDiskMark. Although both have their uses, they also have their limits, notably that they only measure read and write speed for one test size, normally 5 GB in the former and 1 GiB in the latter. As the graph below shows, there are substantial differences in speed between different sizes.

The upper pair of unbroken lines show read and write speeds when operating in TB5 mode over 80 Gb/s to the Mac mini M4 Pro, and the pair below them with broken lines shows speeds when operating in USB4 mode over 40 Gb/s to a MacBook Pro M3 Pro. Calculated overall read/write speeds were 5.2/5.5 GB/s for TB5, and 3.1/3.1 GB/s for USB4. For comparison, Blackmagic returned 4.8/5.2 GB/s, and Amorphous 6.8/5.3 GB/s. Needless to say, the latter is the result being quoted by the manufacturer, despite its write speed looking highly suspect.

Highest read and write speeds were measured with 400 MB size, and there were only small differences once sizes exceeded 600 MB. However, speeds for files below 10 MB were considerably less than 100 MB and larger. Fortunately, Blackmagic Disk Speed Test and AmorphousDiskMark both use sizes in the more linear range above 600 MB, but their results don’t take into account smaller file sizes, which are more common in many real-world circumstances. As the 80th centile write speed was 5.62 GB/s, the write speed reported by Amorphous of 6.8 GB/s doesn’t appear representative.

Caching effects

All those benchmark results are subject to a major caution: they don’t provide any information on caching, used by most faster SSDs to improve performance. This typically uses part of the memory in SLC mode, sacrificing capacity for speed. I’ve seen a figure of 50 GB of cache quoted for one TB5 SSD that I’ve tested, and sure enough, once 50 GB has been written to it, its write speed drops from around 5.5 to 1.4 GB/s.

Few are likely to write more than 50 GB to an SSD in a single continuous session, but for those that do, it’s important to know when the SLC cache is likely to become full, and for write speed to fall to little better than USB 3.2 Gen 2. Neither Blackmagic Disk Speed Test nor AmorphousDiskMark can measure that for you.

Overall impressions

Thunderbolt 5 SSDs are starting to realise their promise of significantly faster read and write performance than even USB4 SSDs. Although TB5 SSDs are supported by a small range of the latest Macs, they should still be faster than TB3 when they fall back to USB4 on other Apple silicon Macs. However, if they’re to be used with Intel Macs, the likelihood is that they will fall further back to USB 3.2 Gen 2.

If you’re likely to stream very large quantities of data to them, more than about 50 GB, then you’ll need to obtain an estimate of the size of their SLC cache, and of their write performance when that is full, or you could be in for a big disappointment. The trouble with TB5 SSDs is that they’re sufficiently fast to fill their cache very quickly, in this case in around 10 seconds when writing at full speed.

Postscript

I’ve gone back to my original article analysing TB5 performance, and the maximum transfer rate it can achieve over its 80 Gb/s works out at 6 GB/s. I therefore conclude that the claimed 6.7 GB/s reported above can only be bogus, although it’s now being claimed by manufacturers and other testing sites. If you see TB5 claimed to exceed 6 GB/s, then don’t trust those figures.