Samsung T7 drives running extremely slow (15" MacBook Pro 2019)

As SSD technology advances (or rather changes) the NAND memory used in SSDs is becoming slower (and also has less endurance, aka number of lifetime writes) so SSD write speeds don't usually end up at the top end of the spectrum. In fact most speed tests reported on these forums many times will show the SSD's write speed to be about half of the read speed.

To make up for the slower NAND memory speed SSDs implement a write cache to make it appear that the SSD is faster, but once this write cache fills up the SSD's speed will drop. How much the speed will drop depends on how the SSD was designed. I have seen some SSDs slow down to 50MB/s and it can take a long time for the write speed to recover. If an SSD overheats the SSD's speed will be throttled until the SSD cools off. The longer the SSD speed test the more likely you will encounter poor write speeds.

Unmount the volumes on the external SSDs (do not eject them since that will cause the drive to lose power) so you can leave the SSDs physically connected and powered on, but they won't have any data transfers or communication with the Mac. With the SSDs unmounted and still connected the SSD still has power so that the SSD's internal maintenance & garbage collections routines have time to work and help the SSD return to normal. After the SSD has been sitting like this for a few hours unplug the SSD and reattach it so you can run another speed test on it.

If the SSDs are nearly full, then that will also cause the SSD write speeds to slow down as the SSD needs to do a lot of behind the scenes work to provide empty blocks for storage (there is a lot of behind the scenes work going on with an SSD).

There may also be a compatibility issue with the newer Samsung SSDs and macOS.

You may want to check the health of the SSDs by running DriveDx. You will need to install a special USB driver so that DriveDx can communicate properly with the USB drives to access their health information. However, some USB drives won't allow the necessary communication to access the health information even when using the special USB driver. Post the reports for your Samsung T7 SSDs here using the "Additional Text" icon which looks like a piece of paper.

Also, maybe Spotlight has decided to index the external drive which can affect the speeds.

Same issue here - two T7's not full, one's rarely used at all, but performance has fallen off a cliff - 30 MB/s. Have two T5's which are older and fuller, and they both still get 400 MB/s. There's something wrong with the T7's - they're even slower than my spinning drives!

I've tried zeroing them out, leaving them connected, partitioning, formatting, and everything else but sacrificing a junior intern to the SSD Gods, but no go. Wish I could return them, but of course they both failed just outside the return window.

Avoid T7's on the mac...not remotely worth the money.

Wonder if this has something to do with it: https://macperformanceguide.com/SamsungT7-2TB.html

I have a similar situation. I bought two identical T7 drives - attached to my Mac mini M1. One performs 600MB/s read and write. The other performs 100MB/s write and 600 MB/s read.

I’ve switched the ports- same results.

Running Big Sur. Both about 40% -50% full.

Only difference is that I have the Photos library on one (the one that performs poorly). I haven’t added any photos in 2 months or more, but maybe there is a connection.

I wish there was a Mac version of magician.

Same experience here, Samsung T7 35 Mb/s read and write on MacBook Air M1. Not a big deal for me using it as backup storage, sure that is a bit puzzling compared to many positive reviews with similar setup. Stay away, agreed.

I think I know what's going on. I repartitioned (not formatted) as HPFS+, then zeroed out the drive with dd. That restored performance. I had the drive encrypted, and I suspect that the internal firmware doesn't handle that well, and saw the drive as 'full' constantly, but can't confirm. Either way, you can restore performance. I've moved to using them just for backup, rather than live/lots of changes/use.

ryanfarber wrote:

what is dd?

edit. nvm assuming its DriveDx

"dd" is a command line utility that has low level access to the drive which can be used to write zeroes or even write bootable .iso image files to a drive (these are just two of the most common use scenarios, but not the only ones). Sometimes macOS and Disk Utility can get confused by a drive and be unable to work with it unless the beginning of the drive has had zeroes written to it in order to destroy the partition table.

Unless you know what you are doing (or are given very explicit instructions to use the command line) just avoid the command line since it is very easy for a person to cause major damage to macOS or wipe out their data (even people with years of command line experience can easily make a mistake and need to restore from a backup). The command line has no safety net.

Yup. The actual command sequence will vary, but it's essentially

cd /Volumes

cd yourvolumename

dd if=/dev/zero of=./delete.txt bs=4096

If you do it in the wrong place it can crash your mac and, well, cause problems. In this case though, I'm not zeroing out the partition table - I just repartition it in disk utility, then zero out the contents of the drive, which unborks the garbage collection/pseudo-trim function in the drive firmware. Alternatively it's possible that repartitioning as HPFS, then dismounting but leaving it plugged in overnight may let the firmware recover the drive sectors automatically (and that'd be a lot safer).

lhotka wrote:

In this case though, I'm not zeroing out the partition table - I just repartition it in disk utility, then zero out the contents of the drive, which unborks the garbage collection/pseudo-trim function in the drive firmware. Alternatively it's possible that repartitioning as HPFS, then dismounting but leaving it plugged in overnight may let the firmware recover the drive sectors automatically (and that'd be a lot safer).

Filling an SSD with zeroes is not a good idea as it causes premature and excessive wear on the SSD since SSDs have a limited number of lifetime writes.

Using Disk Utility to perform a simple "erase" on an Apple SSD which has TRIM enabled definitely zeros the complete SSD since an "empty" SSD during the Disk Utility "erase" (aka partition and formatting) zero all the cells due to TRIM. I don't know if the same thing happens to a non-Apple SSD (or an external SSD or an SSD without TRIM enabled) as I've never tested it (I did test an internal Apple SSD).

If you have problems with Disk Utility erasing or partitioning any drive (HD, SSD, USB stick), then just write no more than 1GB of zeroes at the beginning of the drive to overwrite the partition table and beginning of the drive. You will first need to unmount all volumes on the drive (you don't want to eject the drive). This will usually allow Disk Utility to be able to properly erase (aka partition & format) the drive.

If you want an SSD's garbage collection and maintenance routines to fix things, then you need to supply just power to the SSD and leave the data cable disconnected. Connecting a USB SSD to a USB power supply is one way to power on the drive without any data communication interfering with the SSD's controller. Also some powered USB hubs have a dedicated USB port for charging mobile devices so the dedicated charging port does not allow data transfers.

If that is not enough to fix an SSD issue because the SSD's controller or NAND is having some issue, then it would be better to use the SSD's built-in hardware secure erase feature which will reset the SSD to factory defaults which also fixes some SSD issues and restores any lost performance. The hardware secure erase feature is like flipping a circuit breaker to quickly reset every single NAND cell in the SSD which minimizes the wear on the SSD compared to writing zeroes to an SSD. Performing a secure erase on an external drive may be a bit risky (there are warnings on the page describing procedure -- they may just be overly cautious), but I also think it depends on the SSD's USB controller (some kind of timeout issue with some USB controllers). I've performed a hardware secure erase on several USB connected SSDs without any problems (I've used USB adapters/docks/enclosures using the ASMedia USB chipset). I think some SSD manufacturer's proprietary software may allow a hardware secure erase on a USB SSD, but I am not a Windows user so I am not certain.

Performing a hardware secure erase requires a Linux boot drive and utility unless you use the manufacturer's proprietary app (usually requires Windows). I'm not providing any links here since this isn't your thread and like I said the procedure may be risky on a USB drive. Since you are familiar with the command line you should be able to easily locate the Linux page describing the procedure. Parted Magic is a paid Linux boot utility disk that has a custom easy to use utility for performing this procedure.

Well, yes and no.

Using disk utility to erase the drive does not correct the issue on the T7's - they clearly have a different set of firmware from the T5's. Dismounting but powering on does not trigger garbage collection on T7's if the drive is encrypted.

Modern SSD's have multi-petabyte lifespans, so doing this once or twice doesn't have a practical impact on the device. As I mentioned, I use dd within the repartitioned (not just erased) disk, rather than on the raw device itself - doing that solves the issue without jumping through hoops with the (horrible) samsung software, alternate platforms etc.

The net is that T7's don't play well with filevault, but T5's do. So do SanDisk drives, which is my going-forward solution :-)