Upgrading My Mac’s External SSD
I recently replaced a 4 TB 2.5-inch hard drive with a same-sized SSD, with the goal of making it quieter and faster. Instead, it got much slower. As far as I can tell, there’s nothing wrong with the SSD itself (a Samsung T7). The drive tests fine, and I have half a dozen other drives in this family that all work great.
I think the problem is that I put about 3.5 TB of data on it. I was aware that you don’t want SSDs to be super full, but this particular data set grows slowly, so I thought I’d have several hundred GB of free space for the next few years. But I guess that isn’t enough. The drive started out fast at reading and writing, but after filling it up the writes seemed to take forever. Stibium benchmarked them as slow as 1.6 MB/s, but I think they were actually far lower overall.
Samsung doesn’t make a larger T7 or T9, so I ordered an 8 TB SanDisk. That should be plenty of space, and I’ve long used the 2 TB version of that drive. It’s the only non-Samsung SSD that’s worked reliably for me. Unfortunately, I cannot recommend the new SanDisk, at least not for use with a Mac. It kept spontaneously unmounting in the middle of copying files, whether connected to a Thunderbolt dock (via the provided cable) or to a USB hub. Some Amazon reviews note the same problem, even though it overall has 4.6 stars from 81K ratings. In light testing, it did seem to work when directly connected to my MacBook Pro, but I only have three ports and don’t want to dedicate one to this drive.
I replaced it with a Samsung T5, which in theory is slower than the T7, but in actual use it’s much faster than what I had before, and it seems to be reliable.
Previously:
- USB-C Hubs and My Slow Descent Into Madness
- Upgrading an M4 Pro Mac Mini’s Storage for Half the Price
- Using “tmutil associatedisk” With APFS Destinations
- Mac SSD Performance
- USB-C Is Still a Mess
- The Impossible Dream of USB-C
- RocketStor Drive Dock: More Expensive But Reliable
- Highpoint RocketStor 5212 Thunderbolt Dual Drive Dock
Update (2025-08-15): Rosyna Keller:
I strongly recommend against the SanDisk SSDs. There’s no indication they fixed their data loss problems. One of the symptoms of the data loss problems on macOS was frequent unmounting.
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I had the same issue with a T7 which is almost full. In my case adding a windows extended fat partition of 128Mb made it faster, not sure why it worked (read that suggestion in one of Samsung forum if I remember correctly).
It is not always fast with the windows partition, it sometimes take a couple of seconds before it starts getting faster when I access it.
Hope it helps
I use a 8TB ProGrade Digital USB4 SSD as the main storage on my Mac Studio M1 Ultra. It replaced a Sargent 8TB TB3 drive because the latter was QLC flash and even with backups I prefer the higher performance, reliability and endurance of TLC flash. Both worked flawlessly.
Another drive to consider is the Crucial X10 8TB. I’ve had bad experiences with Samsung and have flipped the bozo bit on them. Crucial is a division of Micron and they fab their own flash, like Samsung and unlike SanDisk which sources from Kioxia (f.k.a. Toshiba). I don’t have the 8TB yet, but I do have 2TB and 4TB Crucial X9, they are great drives.
I recommend you get an NVMe SSD (the WD SN850X is great) and an enclosure like the ASUS TUF A2. External drives are just nowhere near as good as internal ones. The enclosure has built in thermal pads so the whole thing acts like a heat sink, and it's 20Gbps, so if you found the T7 to be fast enough, the enclosure should suffice.
I had no idea some drives didn't randomly disconnect on Mac after a while (unless connected without dongle and while the MacBook is connected to power directly — using two ports out of my two).
Is there any way to find them? Or should one just stick to what Mac bloggers certify as usable?
I had a problem with an SSD randomly dismounting. The SSD was from an MacBook Air that I’d put into a USB enclosure. The dismounting only occurred when I copied large amounts of data. I narrowed the problem down to the drive getting too hot. The problem went away once I solved that.
@Saurabh Thanks. Good to know for the future. For this particular drive, I don’t need a lot of speed so even the T5 is fine.
@Alexandre Yeah, this has been a problem with certain USB hard drive enclosures for a long time (see links above) and seems super common with SSDs. Unfortunately, I haven’t seen it discussed much.
@Benedict How did you prevent the drive getting too hot? Did you previously have it running in an area with no ventilation?
Seconding @saurabh. External drives all seem to be bottom tier, Best Buy consumer-grade crap. “Pro-sumer” isn’t exactly a thing in the storage world but an internal ssd + Thunderbolt is basically that.
A little late but I agree completely with using a proper drive in an external enclosure. That's all I ever use. Cheaper, more reliable, faster, just better all around.
Interesting observation. I never had problems with external Samsung USB SSDs on my Macs. I have a T5 and several T7s (Shield). But I only use them for Time Machine and as archival drives for data I only use infrequently. Therefore, it's quite possible that I just haven't noticed the performance degradation yet.
Two things I'd check first are firmware upgrades and possibly a defective USB cable. I believe Samsung only supports doing FW upgrades on Windows though.
If I had to use an external drive permanently as an extension of the internal storage, I would probably go for a more expensive Thunderbolt or USB4 enclosure from a reputable brand. They do seem to support TRIM reliably and tend to have better cooling as well.
@Dan The T7 performed great again with the same cable after reformatting it but not filling it up as much. I also tried it with other cables and a direct connection to the Mac when it was “full” and it was still super slow.
I would look into upgrading the Samsung FW then, if it hasn't been done recently. It's not uncommon for Samsung SSDs to receive several FW upgrades, even years after the product has been first released. They usually address performance or compatibility problems.
I use ACASIS 40Gbps M.2 NVMe SSD Enclosure with an m.2 ssd from crucial.
It's connected via Thunderbolt 4 to my mac mini with M2 pro, it's rock solid, never disconnects and it's almost as fast as internals SSD.
Samsung had issues with their SSDs in the past that required firmware upgrades, so I think it's a good idea to upgrade their firmware regularly. I just run Magician on all PCs that use Samsung SSDs. There's a Mac version, afaik it can upgrade SSD firmware, but I've never used it.
What kind of clown world do we live in, where my SSD might need a firmware upgrade? Tech is making me tired…
Cynicism aside, I also have a T7, love it. But perhaps if you need to store that amount of data, reliably and frequently accessible, the glorified thumb drive is not the right tool for the job
What makes you all think the T7’s slow performance when near-full is a firmware issue and not just a result of using triple-bit multi-level cells?
Wow, installing Samsung Magician on a Mac was a big mistake. Can't end the installer without restarting the computer. Installs kexts that obviously don't work with standard system settings. AB-SO-LUTE worst non-Mac UI, can't quit the program from menu, keyboard or even the [X] on the top right, you must use the menubar icon, where (or in settings of the app) you also must disable starting at startup.
Had to google how to uninstall, too. 1. There's a cleanup script in ~/"Library/Application Support/Samsung/Samsung Magician/" called CleanupAll.scpt. Double-click to open, click Play to run. 2. Run in Terminal: "sudo kextcache --clear-staging". 3. Remove preferences which are at "Library/Preferences/com.samsung.magician.*.plist". 4. Now there's a only a couple of empty directories and links to recently used files, which I guess you can leave.
Oh and I forgot the most important part: it didn't even see the attached Samsung Portable SSD T7! But maybe that was because I didn't activate the kexts.
The best Samsung External Portable SSD so far (T1, T3, T5, T5 EVO, T7 series, T9 and X5) is the T5 hands down (note that is T5, not the T5 EVO). A new one named P9 will be announced soon. Other good one is the OWC Express 1M2 8 TB (USB4). Note the size, because that could make a huge difference in performance. Such 8 TB and only it (not the 4TB) can sustain read and write speed across all capacity. That is amazing:
TESTED, OMG: OWC Express 1M2 USB4 SSD Trounces the Fastest Thunderbolt 3 SSD
Look at those crazy-fast speeds for both writes and reads, writing the entire 8TB capacity (2 runs shown).
No external SSD I have ever tested can compete with this outrageously fast performance. Not only that, the consistency is breathtakingly solid across the two runs. Remember, this is writing and reading the entire 8TB capacity!
Average Write: 3076 MB/sec
Average Read: 3429 MB/sec
https://macperformanceguide.com/blog-2023-12.html#20231207_1540-OWC-EnvoyExpress1M2
And soon a new OWC Express 1M2 USB4 v2 16 TB version will be released.
Finally, beware SanDisk 81K ratings in Amazon. They are not of any SanDisk SSD in particular, but of all their storage devices, which is an utterly misleading marketing trick. And beware SanDisk erasing disk contents and current lawsuit about it. The firmware update has not fixed it for some users. Shocking.
"What makes you all think the T7’s slow performance when near-full is a firmware issue and not just a result of using triple-bit multi-level cells?"
I don't think that; I just think it is generally a good idea to update Samsung SSDs' firmware regularly due to their history of having serious firmware issues.
+1 to Dmitry with Acasis - get the USB-4 enclosure, put a Samsung NVMe drive in it (I put in the 4TB 990pro) and enjoy 0 disconnects and 3GB/s speeds, imperceptibly slower than the internal drive on a MBP. The enclosure gets hot, but it doesn't matter.
As many people said, use external enclosures with m2 SSDs, they’re more reliable and waaaay faster. If you find it on offer and you care more about size than performance (I use it for Time Machine) get a Samsung 870 QVO 8TB with an external SATA enclosure. It does about 200MB/s read/write … but it’s 8TB.
For the enclosures the Sabrent and ugreen ones are great, go thunderbolt if you want to splurge for extra speed and reliability, or if you want to be able to update the SSD’s firmware (in Windows).
Although if you don’t want to connect them directly to the mac you will need either a good USB hub (what? Doesn’t exist…) or a thunderbolt one. If the hub resets it doesn’t matter how good the other components are…
Regarding T5 vs. T7: It seems both generations use TLC memory (triple-level). Some websites claim, that the T5 has internal DRAM, while the T7 appears to be DRAM-less (Host Memory Buffer) design. HMB is quite common for lower budget internal and external SSDs nowadays. Maybe for some reason the macOS USB drivers have problems with this architecture? Of course, I'm just guessing.
@Michael yep, it was in an unventilated cupboard. Even when it was in a ventilated room it still failed but less frequently. My guess is that the enclosures aren’t designed with heat in mind. After the initial copy I haven’t had any problems, presumably because not much data is transferred to it now.
Do not ever buy Crucial drives -- they constantly unmount in the middle of the write, which causes file system damage and macOS reports that apfs (encrypted) is broken.
Bite a bullet, and get yourself thunderbird m² enclosure with the 4tb m² nvme drive. I got rid of all possible problems I had.
I bought Acasis (https://www.amazon.com/ACASIS-Enclosure-Compatible-Aluminum-External/dp/B0BB74BQVN) when it was on sale for $55 or so. Happy with my m1 Mac Studio.
I agree that an external enclosure is the way to go, but in my experience, choosing the right chipset is equally important for reliability and performance.
Unfortunately, it's not always easy to determine which chipset is used in a given enclosure. Below are some USB chipsets I have come across:
⭐ ASMedia ASM2464 # USB4
👎 ASMedia ASM2362
👎 JMicron JMS583
- Most popular
- Unstable under load due to excessive power draw which causes overheating
⭐ Realtek RTL9210(B)
- Stable performance
- Supports NVME and SATA
Unfortunately, it seems a common problem that some (all?) Macs will only connect to various USB spec external storage devices at 10 Gb/s speeds, even if the devices themselves support up to 40 Gb/s.
Easiest/dumbest solution: use Thunderbolt storage devices.
Yes I only use OWC external drives. Usually with their SSDs, but sometimes just the enclosure with something else. Never had a problem.
