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Ric Ford

MacInTouch
I'm trying to reinstall macOS on an iMac (27-inch, Late 2013), prior to resale. I've already wiped the 3TB Fusion drive. I've tried various versions of macOS, both from USB flash installers and via Internet Recovery, but they always fail with an error such this one from High Sierra...
Apple has now hidden/deleted information about defective iMac 3TB Fusion drives in that timeframe that required a special replacement program. You might want to start there.

Otherwise, since High Sierra doesn't support APFS on Fusion drives, it seems like a scenario that may be prone to problems. Here's what I suggest if you sort out the question of defects above:
  1. With the internal storage "defused", check for SMART errors on both SSD and hard drive with a utility such as DriveDX.
  2. If you're sure there are no defects or hardware problems, boot a normal macOS Sierra 10.12.6 system and format the Fusion drive as HFS+, then try installing macOS Sierra. (Alternatively, you could try using macOS 10.14.3 Mojave instead, but I would use Sierra.)
  3. If that doesn't work for any reason, defuse the SSD and hard drive, format the hard drive in HFS+ format, and install macOS Sierra on that.
 


I'm trying to reinstall macOS on an iMac (27-inch, Late 2013), prior to resale. I've already wiped the 3TB Fusion drive.
... Has anyone seen anything like this before? Any ideas to get it to install?
For checking disk hardware, Disk Utility is not particularly useful. I use SMART Utility from Volitans, but DriveDX and other products can report SMART details.

Installing Mojave on your machine might make it more valuable. Just this morning I performed a clean install of Mojave (10.14.3) on a Late 2013 27" iMac. The 1.1TB Fusion Drive was still 'fused' and working before this process. SMART Utility indicated both drives were healthy.
  • Created a USB external volume, Install macOS Mojave, by downloading a fresh copy of the Mojave installer and used creatinstallmedia to make a bootable USB installer volume.
  • Used Command-R boot to start the iMac.
  • Selected Disk Utility and did a simple Erase of the fusion volume.
  • Installed Mojave.
  • Got a clean macOS startup.
Several factors contributing to my success include using SMART Utility to verify both the hard drive and SSD, not overthinking the fusion drive business, just selecting MacintoshHD and clicking Erase using the default parameters.

The installation seemed to take quite a while before actually starting the install progress bar. I guess it was updating the on-disk structures of the internal fusion drive which is now an APFS fusion drive.
 


Apple has now hidden/deleted information about defective iMac 3TB Fusion drives in that timeframe that required a special replacement program. You might want to start there.
Otherwise, since High Sierra doesn't support APFS on Fusion drives, it seems like a scenario that may be prone to problems. Here's what I suggest if you sort out the question of defects above:
  1. With the internal storage "defused", check for SMART errors on both SSD and hard drive with a utility such as DriveDX.
  2. If you're sure there are no defects or hardware problems, boot a normal macOS Sierra 10.12.6 system and format the Fusion drive as HFS+, then try installing macOS Sierra. (Alternatively, you could try using macOS 10.14.3 Mojave instead, but I would use Sierra.)
  3. If that doesn't work for any reason, defuse the SSD and hard drive, format the hard drive in HFS+ format, and install macOS Sierra on that.
My iMac was sold too late to qualify for the 3TB hard drive replacement program.

I de-fused and ran TechTool Pro to check the drives. The SSD was clean, but the hard drive reported several SMART values that TechTool Pro interpreted as warnings.

I gave up and shipped it off for recycling. The graphics were failing anyway. (What surprised me was that there were sites willing to give me money for an iMac with failing graphics!)
 



I have a Mac Mini, late 2018, and two Crucial MX300 SSDs and a Crucial MX500 SSD in a Thunderbolt box.
  • All are 500GB, all have out of date firmware, and 2 of the 3 are giving SMART drive errors that Crucial says will be fixed by the firmware updates.
  • Crucial only distributes firmware updates as ISO image files, but my only DVD drive is USB
  • The best solution I have found seems to be to create a virtual OS using Linux, and use that to make the ISO file into a bootable USB flash drive. Alternatively, I have a spare small SSD I could put the ISO on for that purpose if needed and access the drive by Thunderbolt.
  • I know the words, but I have never walked the whole walk.
  • I have Parallels and they provide a way to make the virtual Linux OS
  • but I am less sure from there about moving the ISO image into that OS and then out again as a bootable drive.
I'm hoping someone can point me to either a step by step guide or even a simpler way to get to the goal line.

As always, MacInTouch is not just the best source of Mac info and help, but pretty much the only place I go to. And Ric truly a hero for not just keeping it going but continuing to make it better.

Thanks
 


Ric Ford

MacInTouch
... I'm hoping someone can point me to either a step by step guide or even a simpler way to get to the goal line...
Something like this should work:
  1. Download the .iso file(s) containing the bootable updater(s)
  2. Hook up your USB DVD drive and get some blank discs.
  3. Hopefully ImageBurner can burn the .iso to an optical disc
  4. Hopefully you can boot off the optical disc when it's burned and loaded into the USB DVD drive (which might take some hoop-jumping with the new T2-based Mac Mini... or might not work... but worth a try)
  5. If you can't boot from the disc (via Option boot), do you have another Mac that can?
  6. If you can boot from the updater disc, it should be able to see the SSDs in a Thunderbolt box... and update them.
 


Ric Ford

MacInTouch
Hopefully you can boot off the optical disc when it's burned and loaded into the USB DVD drive (which might take some hoop-jumping with the new T2-based Mac Mini... or might not work...
I tried unsuccessfully to do this with a 2018 MacBook Pro - boot repeatedly failed, in Kafka-like ways, even after turning off startup security and enabling external boot. (I can't even boot a current Linux Mint Live USB stick that works fine on several 2015 and older MacBook Pros. I think Apple may have killed Linux booting with a Mojave update at some point.)

So... do you have any friends with Windows PCs? (Or an older Mac?)
 




Even on an old iMac, the Micron updater is now different.

I had no problem updating my MX500 back in June 2018 to M3CR022 on my mid-2011 iMac on macOS 10.12.6, as the drive was on the internal SATA bus and I have the internal SuperDrive; I made the ISO CD-R, booted from it, it updated, no problem.

Today, this thread prompted me to check, and I see the Dec. 2018 firmware update, M3CR023. I dutifully followed the exact same procedure, but the CD would not boot. After looking at the comments in their KB entry, I saw that instead of previously option-booting into Windows, people now had to select EFI Boot (contrary to the instructions), which gives different screens, but ultimately seems to work.
 



Something like this should work:
  1. Download the .iso file(s) containing the bootable updater(s)
  2. Hook up your USB DVD drive and get some blank discs.
  3. Hopefully ImageBurner can burn the .iso to an optical disc
Another option might be to use balanaEtcher (aka “Etcher”) to write the ISO to a USB drive. Still doesn’t solve the T2 boot issue, but will boot faster, and you can always re-use the USB flash drive for new updates or other data storage.

I use Etcher to create Linux install media from ISOs, so I can verify that it works for ISO to flash drive.
 


I have a Mac Mini, late 2018, and two Crucial MX300 SSDs and a Crucial MX500 SSD in a Thunderbolt box.
  • All are 500GB, all have out of date firmware, and 2 of the 3 are giving SMART drive errors that Crucial says will be fixed by the firmware updates.
  • Crucial only distributes firmware updates as ISO image files, but my only DVD drive is USB
  • The best solution I have found seems to be to create a virtual OS using Linux, and use that to make the ISO file into a bootable USB flash drive. Alternatively, I have a spare small SSD I could put the ISO on for that purpose if needed and access the drive by Thunderbolt.
There are now macOS applications to write a bootable ISO to a USB drive. A couple of the Linux distributions have directions.

Fedora Media Writer
While suggesting downloading Fedora, the green button at top downloads Fedora Media Writer. The other iSO download links are for the OS. And the app has an easy way of pulling a Red Hat ISO but can optionally select a ISO file on the local file system. I'm not sure if Fedora's tool is signed with an Apple developer signature or not. May have to 'approve' it as OK to run.

Create a bootable USB stick on macOS | Ubuntu tutorials
The tool they point to is Etcher. (Step 3 - you prep the USB drive.) Probably does help to turn it into a GUID drive before installing the ISO.

Whichever tool, it's probably a good precaution to format the USB drive into GUID state first.

Both are far less drama than trying to get a Linux VM up and running just to write an ISO to a USB drive.

In the process of lowering the boot security while in Recovery mode's "Startup Security Utility", it is a good step to double-check that settings are in effect by rebooting back into Recovery mode again to see if it's still at the lowered setting (both external booting allowed and all the way down to "no security").

One possible issue will be if the highly pruned-down OS that runs on the firmware installer has the drivers necessary for Thunderbolt. I haven't checked on these lately, but years ago some of these firmware upgrade tools were stripped-down FreeDOS variants. That probably won't work. It should be a more modern Linux/BSD foundation that can boot with EFI/UEFI and doesn't freak out with Thunderbolt present. Some of these installers are hard-coded to probe at the internal drives (as opposed to looking at the drives connected via SATA controller(s)).
 


I have a Mac Mini, late 2018, and two Crucial MX300 SSDs and a Crucial MX500 SSD in a Thunderbolt box.
  • All are 500GB, all have out of date firmware, and 2 of the 3 are giving SMART drive errors that Crucial says will be fixed by the firmware updates.
  • Crucial only distributes firmware updates as ISO image files, but my only DVD drive is USB
  • The best solution I have found seems to be to create a virtual OS using Linux, and use that to make the ISO file into a bootable USB flash drive. Alternatively, I have a spare small SSD I could put the ISO on for that purpose if needed and access the drive by Thunderbolt.
  • I know the words, but I have never walked the whole walk.
  • I have Parallels and they provide a way to make the virtual Linux OS
  • but I am less sure from there about moving the ISO image into that OS and then out again as a bootable drive.
I'm hoping someone can point me to either a step by step guide or even a simpler way to get to the goal line.

As always, MacInTouch is not just the best source of Mac info and help, but pretty much the only place I go to. And Ric truly a hero for not just keeping it going but continuing to make it better.

Thanks
Could some of your boot-from-external-drive issues be caused by the T2 chip not being configured to allow booting from an external drive with nonsigned OSes? The defaults in Secure Boot are "Full Security" (boot only the current, signed macOS version) and "Disallow booting from external media."
 


Ric posted a reference to this drive enclosure February 18, 2018 in "Products" news.
AnandTech said:
Plugable USBC-NVME Tool-Less NVMe SSD Enclosure Capsule Review
The Plugable USBC-NVME is perfect for consumers who need to mount and dismount M.2 NVMe SSDs frequently. An example would be a scenario where a user needs to quickly identify the contents in a M.2 NVMe SSD prior to formatting for installation in a PC. The tool-less aspect is a major contributor to this aspect. The downside is that the thermal performance is not as good as that of the MyDigitalSSD M2X.The M2X is more suitable for use-cases where the installed SSD needs to be swapped out very rarely. Despite using the same bridge chip (JMicron JMS583), the enclosures excel for different use-cases.

As of the time of posting this review, Plugable has sold out of their initial stock of the USBC-NVME enclosure. The next shipment is on the way, and should be available again on Amazon for USD 50 shortly. The pricing is a bit higher than the USD 40 for the MyDigitalSSD M2X. Consumers can go in for either enclosure based on their intended use-case.
 


There are now macOS applications to write a bootable ISO to a USB drive. A couple of the Linux distributions have directions.
Fedora Media Writer ...
Create a bootable USB stick on macOS | Ubuntu tutorials ...
I did a quick check of both methods to make a bootable USB drive with my 2018 Mac Mini running macOS 10.14.3. The Ubuntu tutorial worked to produce a bootable Ubuntu drive. I did check that the drive, when booted, would do at least elementary Linix operations (command line and Firefox).

My brief try with Fedora Media Writer wasn't as successful, but I didn't take time see what caused the problem.

One point on both of the tests was that when booting with the option/alt key, the normal Mac startup drive showed up with two other drives labeled just as "efi". I had to try each one to see which one was the Linux drive.

Another point is that it is absolutely trivial to set up Linux (Ubuntu is what I tried) with Parallels 14. I didn't really need it, since the Mac has all the Unix tools I've ever needed, but if there's something weird in Linux I need, I now have it.
 


I just updated an MX100 from a USB drive using an EFI bootloader. (I upgraded it to MU02 a few years ago and MU03 yesterday using this method.) There's a good tutorial on the MacRumors forum here.
 


As a quick aside, I spent a good amount of time installing Boot Camp on my old Mac Pro just so I could update my MX300. It's a pain that on my Mac Mini, I have to disconnect external drives to install Boot Camp (why!?), because that's where I would want to install Windows!
 


Another point is that it is absolutely trivial to set up Linux (Ubuntu is what I tried) with Parallels 14. I didn't really need it, since the Mac has all the Unix tools I've ever needed, but if there's something weird in Linux I need, I now have it.
It's quite simple, perhaps even trivial, to do so in VirtualBox, too.
 


Ric Ford

MacInTouch
Another point is that it is absolutely trivial to set up Linux (Ubuntu is what I tried) with Parallels 14. I didn't really need it, since the Mac has all the Unix tools I've ever needed, but if there's something weird in Linux I need, I now have it.
It's quite simple, perhaps even trivial, to do so in VirtualBox, too.
While it does seem easy enough to install Linux in a VirtualBox VM, configuring it to actually access Mac folders and files and the Internet seemed to be non-trivial, the last time I tried it. Has anyone actually updated SSD firmware from a virtual machine?
 


Ric Ford

MacInTouch
To the best of my knowledge, TRIM does not work over USB, so that shouldn't be involved.
I did a little test of that, using Disk Utility > First Aid:

Apple internal SSD:
...​
Checking Journaled HFS Plus volume.​
Checking extents overflow file.​
Checking catalog file.​
Checking multi-linked files.​
Checking catalog hierarchy.​
Checking extended attributes file.​
Checking volume bitmap.​
Checking volume information.​
Trimming unused blocks.​
Samsung T5:
...​
Checking Journaled HFS Plus volume.​
Checking extents overflow file.​
Checking catalog file.​
Checking multi-linked files.​
Checking catalog hierarchy.​
Checking extended attributes file.​
Checking volume bitmap.​
Checking volume information.​
Trimming unused blocks.​

See also:
Apple Community said:
Does Disk Utility do TRIM for a 3rd party…
As a test, I just turned off TRIM on my Crucial M500 running Mountain Lion and rebooted. In System Information, TRIM was no longer enabled for the SSD. I rebooted into Single User Mode and ran the fsck command. No Trimming of unused blocks appeared or occurred. I turned TRIM back on using TRIM Enabler, rebooted, checked TRIM status in System Info again and it was active. Rebooted yet again into Single User Mode, ran fsck and trimming unused block appeared as expected.

I tried something similar but this time booting from another internal OWC SSD, turning TRIM on and off and using Disk Utility on the M500 (since fsck only works on the boot drive). I got the same results.
AnandTech said:
Samsung Portable SSD T5 Review
Support for TRIM is a much more interesting feature, given that neither the T1 nor T3 supported it. Though Samsung doesn't officially claim TRIM support for the T5, we formatted one of the drives in NTFS to verify the status. We were pleasantly surprised to find that TRIM was enabled. It is likely that the new ASMedia bridge chip has contributed to the availability of this feature.
While Windows clearly does support Trim over USB, as described above, George contends that Macs still do not support Trim via USB, though neither of us has been able to conclusively confirm whether or not that's the case, thanks to Apple's omission of any relevant documentation, in spite of all the confusion expressed in the company's own "support" forum.
 


I suppose Apple won't specify, but I wonder if they use MLC or TLC (hopefully not QLC) SSDs? I ask because, given the soldered in/non-replaceable/disposable nature of today's machines, I would want as high write endurance as possible. When I bought SSDs for my 2011 MacBook Pro, I made sure to get MLC drives. I have no idea what is in my 2015 MacBook Pro.
 


Ric Ford

MacInTouch
I suppose Apple won't specify, but I wonder if they use MLC or TLC (hopefully not QLC) SSDs? I ask because, given the soldered in/non-replaceable/disposable nature of today's machines, I would want as high write endurance as possible. When I bought SSDs for my 2011 MacBook Pro, I made sure to get MLC drives. I have no idea what is in my 2015 MacBook Pro.
You can try starting with iFixit teardowns, which identify flash module info, such as manufacturer, capacity and part number.
 


I suppose Apple won't specify, but I wonder if they use MLC or TLC (hopefully not QLC) SSDs? I ask because, given the soldered in/non-replaceable/disposable nature of today's machines, I would want as high write endurance as possible.
Overall drive endurance isn't solely a factor of number of bits per cell. For relatively small capacities (e.g, ~ sub-64GB), it plays a bigger role. However, as the drive capacities go dramatically up, it can be less of a factor.

Larger capacity can be leveraged to keep the end user capacity the same and crank the "over provisioning" allocation much larger. That in turn can be used to spread the load around more, get better data recovery (checksum restore), and cache more data that presents as highly write-active at a different bit storage level - there are some SSD controllers for TLC and QLC that can tag a subset of the NAND area to store data SLC-style. Pragmatically, throw away the potential 2-3 bits storage to get more endurance for 'hot', mutating data.

So, if you take a 32GB area and "under store" by 1/3 or 1/4, you get a 10GB or 8GB 'hot' data area. That won't let the drive maker drive to the lowest possible $/GB ratio, though. That will work for more normal workloads.

For applications that deliberately try to mutate most of the drive data (a cache drive for a database or network storage server with a normal percentage of active writes), that approach won't work as well. When this "hot" spot area gets a bit worn, they can simply shift the target area to someplace else and stuff 'well known', highly static data onto these "almost worn out" cells.
When I bought SSDs for my 2011 MacBook Pro, I made sure to get MLC drives. I have no idea what is in my 2015 MacBook Pro.
TLC (and up) was still ramping up in 2015. At one point, some tech press/makers expressed hope that a standard endurance testing methodology would appear, and "drive endurance" would be commonly reported, like MTBF or other basic specs. Apple obviously wasn't (isn't) interested in that. If they were/are doing a better than average job, it would help justify their higher-than-market $/GB. If it is incrementally below average, then Apple may be sailing the Titanic into the iceberg field in a couple of years.

For mainstream workloads, modern SSDs are not brittle.
 


Overall drive endurance isn't solely a factor of number of bits per cell. For relatively small capacities (e.g, ~ sub-64GB), it plays a bigger role. However, as the drive capacities go dramatically up, it can be less of a factor.
The controllers are continually being improved, but the number of bits per cell is a big determining factor.

For example, the cells in my Samsung 850 Pro (MLC) were rated for 6000 P/E cycles. The Samsung 850 EVO (TLC) was rated for 2000 cycles. Both used the same manufacturing process.

Everything else being equal, MLC is going to have better endurance than TLC, and much better than QLC.

An interesting point about 3D V-NAND is the die size. The endurance of planar NAND had steadily been getting worse every time the manufacturing process shrunk the die size. Controller magic was able to compensate to keep the TBW ratings up. When Samsung went to 3D V-NAND, they also went back to the older 40nm process, which has much higher endurance than the 16nm to 20nm process that was being used for planar NAND. The larger die size + newer controller logic turned into really astounding endurance.

Discussions of TLC being good enough for 'typical' usage is irrelevant to me - my usage isn't typical, and MLC helps mitigate the disposable nature of today's machines. Endurance/reliability is more important to me than $/GB. My Pro model was well worth the extra $50 (or whatever it was) over the EVO model. For what Apple charges for them, they should be SLC.
 


Cabling is confusing both for the hardware and the protocols. So my response to updating a fusion drive is to use an external SSD and generally abandoning the internal fusion driver or possibly cloning the main external drive to the fusion hard disk as a backup.

This late 2015 iMac had Thunderbolt 2 ports. One could use a Samsung T5, but that would leave considerable unused speed. It there a 256 or 500GB SSD and enclosure that would run faster than the T5 but not so costly as the X5? It looks like one could get a USB3 Gen 2 enclosure using Thunderbolt 2 cabling and put an SSD with a 6 gig SATA interface in it.

Too many choices without having descriptions that have information in them that I at least can understand.
 


Ric Ford

MacInTouch
This late 2015 iMac had Thunderbolt 2 ports. One could use a Samsung T5, but that would leave considerable unused speed. It there a 256 or 500GB SSD and enclosure that would run faster than the T5 but not so costly as the X5? It looks like one could get a USB3 Gen 2 enclosure using Thunderbolt 2 cabling and put an SSD with a 6 gig SATA interface in it. Too many choices without having descriptions that have information in them that I at least can understand.
USB 3 is perfectly fine for a standard SSD, as it offers 5 Gbps. SATA III is only 6 Gbps, and standard SSDs aren't going to lose much on USB 3 (assuming a decent enclosure, as with the Samsung T5 or SanDisk Extreme Portable SSD).

Thunderbolt is more appropriate for SSDs in a striped RAID (e.g. OWC Thunderbay 4) and for NVMe SSDs (e.g. Samsung X5), which can be much faster than SATA ones.
 


Be careful; I believe the Crucial MX500 is not backward-compatible with SATA2 interfaces. The 2010 Mini uses the Nvidia chipset and requires either a true SATA2 SSD (like those sold at Macsales.com) or the excellent Samsung 860 EVO (which is SATA3 but backward-compatible). The SanDisk Plus SSDs also exhibit the bad behavior (if I recall correctly). If you uses one of the non-compatible drives in the 2010 Mini, you end up with SATA1 performance.
I'm considering putting an SSD in my retired SATA2 iMac to have a Snow Leopard machine "just in case." Where would I find information about SATA2 compatibility? Is that something that's documented in the manufacturer's specs, or a trial and error type of thing?
 


Ric Ford

MacInTouch
I'm considering putting an SSD in my retired SATA2 iMac to have a Snow Leopard machine "just in case." Where would I find information about SATA2 compatibility? Is that something that's documented in the manufacturer's specs, or a trial and error type of thing?
The manufacturer may or may not provide that information readily. I always look when I write up SSD products for MacInTouch and I typically include that data if it's available.

Samsung has been better than Crucial in supporting older SATA standards.

One consideration, if you're not using the retired iMac frequently: a hard drive may have better data retention than an SSD (though there are a lot of variables). And Snow Leopard actually runs well on a hard drive, unlike OS X 9 and later.
 


The manufacturer may or may not provide that information readily. I always look when I write up SSD products for MacInTouch and I typically include that data if it's available.

Samsung has been better than Crucial in supporting older SATA standards. One consideration, if you're not using the retired iMac frequently: a hard drive may have better data retention than an SSD (though there are a lot of variables). And Snow Leopard actually runs well on a hard drive, unlike OS X 9 and later.
The first place you should go for this is macsales.com and look for the SSDs that are compatible with your iMac. If OWC shows only 3G SSDs, then either buy theirs or a Samsung 860 (as Samsung's SSDs are backward-compatible with older HD controllers that expect 3G and 1.5G drives). PNY's SSDs also have this feature. SanDisk's do not. Regardless of which SSD you choose, backup!
 


Ric Ford

MacInTouch
The first place you should go for this is macsales.com and look for the SSDs that are compatible with your iMac. If OWC shows only 3G SSDs, then either buy theirs or a Samsung 860 (as Samsung's SSDs are backward-compatible with older HD controllers that expect 3G and 1.5G drives). PNY's SSDs also have this feature. SanDisk's do not. Regardless of which SSD you choose, backup!
Actually, I wouldn't buy a PNY SSD if you paid me, and I prefer Samsung and Crucial SSDs to OWC's tricky data-compressing Sandforce controllers. (I'm not sure whether you remember the OWC firmware update fiascos from a while back, and there were some other update issues, though I've also had some working fine long-term.)
 


Actually, I wouldn't buy a PNY SSD if you paid me, and I prefer Samsung and Crucial SSDs to OWC's tricky data-compressing Sandforce controllers. (I'm not sure whether you remember the OWC firmware update fiascos from a while back, and there were some other update issues, though I've also had some working fine long-term.)
I've had a few recent PNYs that have shuffled off their mortal coil after the (2-year?) warranty. As Samsungs have 3-year warranties and the prices are actually less than the best CS1311 PNY unit, I've switched.
 


I've had a few recent PNYs that have shuffled off their mortal coil after the (2-year?) warranty. As Samsungs have 3-year warranties and the prices are actually less than the best CS1311 PNY unit, I've switched.
My experience with a PNY SSD suggests that Crucial or Micron is a better choice.
 


The manufacturer may or may not provide that information readily. I always look when I write up SSD products for MacInTouch and I typically include that data if it's available.
Samsung has been better than Crucial in supporting older SATA standards.
One consideration, if you're not using the retired iMac frequently: a hard drive may have better data retention than an SSD (though there are a lot of variables). And Snow Leopard actually runs well on a hard drive, unlike OS X 9 and later.
I'm not going to buy an SSD, as this is just a "what if I need to open a file/run an app from the distant past" exercise (and this hasn't come up in the 2+years since I retired the iMac). Any files/apps on the iMac would be redundantly backed up on multiple drives in multiple locations, and I still have my Snow Leopard install DVD, so data retention isn't an issue.

I do have multiple SSDs laying around, though, so once I finish moving to Mojave I'll have a SanDisk SSD Plus, an Adata SU800, a Crucial M4 and a WD Blue 3D that I could repurpose. I'll have to look into which of those would be best.
 


USB 3 is perfectly fine for a standard SSD, as it offers 5 Gbps. SATA III is only 6 Gbps, and standard SSDs aren't going to lose much on USB 3 (assuming a decent enclosure, as with the Samsung T5 or SanDisk Extreme Portable SSD).
Thunderbolt is more appropriate for SSDs in a striped RAID (e.g. OWC Thunderbay 4) and for NVMe SSDs (e.g. Samsung X5), which can be much faster than SATA ones.
I was thinking that no external drive could be as fast as the internal SSD, but how about a Thunderbolt 3 striped RAID using NVMe SSDs?

For reference, the internal SSD in my iMac is connected via 4 lane NVMExpress with link speed 8 GT/s, which Wikipedia says is 3.94 GB/s throughput. Thunderbolt 3 is supposed to be 5 GB/s.
 


I was thinking that no external drive could be as fast as the internal SSD, but how about a Thunderbolt 3 striped RAID using NVMe SSDs?
For reference, the internal SSD in my iMac is connected via 4 lane NVMExpress with link speed 8 GT/s, which Wikipedia says is 3.94 GB/s throughput. Thunderbolt 3 is supposed to be 5 GB/s.
I have a Mac Mini 2018 with a 1TB internal drive, a RAID4 OWC Express 4M2 4-Slot M.2 NVMe Thunderbolt enclosure, and a RAID5 OWC ThunderBay 4 RAID-Ready (JBOD) Thunderbolt enclosure.

The 4M2 has 3 Samsung 970 PRO 500GB drives and a single Samsung 970 EVO 500GB drive (the parity drive).

The ThunderBay has 4 2TB WesternDigital Red NAS drives.

The RAID settings are those recommended by SoftRaid for the SSD's and HD's. Here are the speeds as listed by Blackmagic Disk Speed Test 3.2 rounded to nearest 10MB/s:

DriveWriteRead
MacMini2018_1TB_Internal_SSD2670 MB/s2730 MB/s
MacMini2018_1.5TB_OWC_4M2_RAID4930 MB/s2000 MB/s
MacMini2018_6TB_OWC_ThunderBay4_RAID5290 MB/s360 MB/s
 



I was thinking that no external drive could be as fast as the internal SSD, but how about a Thunderbolt 3 striped RAID using NVMe SSDs?
We covered this earlier (I think in this thread), but the problem with the OWC 4M2 is that it only allocates a single PCIe lane per M.2 SSD slot, severely hampering the performance of each blade, and the overall performance unless all 4 slots are populated. And then there's another limit (see below).

For reference, the internal SSD in my iMac is connected via 4 lane NVMExpress with link speed 8 GT/s, which Wikipedia says is 3.94 GB/s throughput. Thunderbolt 3 is supposed to be 5 GB/s.
So, apparently, on a Thunderbolt 3 port, the max speed available for data transfer is about 22 Gbps. I'm not entirely clear on the technical reasons why, but there are references to this available here:
So, the max transfer rate you would see on an external Thunderbolt storage device would be about 2,700 MiB/s. There are internal SSD's that can exceed this transfer rate.
 



Ric Ford

MacInTouch
Here's a warning for others purchasing a new SSD: I just bought a 2TB SanDisk Extreme Portable SSD and a 500GB Samsung T5. As I always do, I used SoftRAID's Certify feature to test them prior to putting them into production (one for backup, one for a photo library). The Samsung T5 tested fine, but the SanDisk Extreme Portable failed certification with write errors.

I tried a second time after removing and replugging the cable a few times, but it failed again, so I'm going to have to send it back to Amazon, and I wanted to let others know, because this type of failure may not be obvious unless you do something like this certification procedure.

DriveDX didn't show any errors in the SMART data, so I don't know where the problem is - possibly the cable, but it's defective, wherever the cause lies. I have another 2TB SanDisk Extreme Portable that I bought previously that hasn't shown any problems, but I'll probably enable Carbon Copy Cloner's "Find and replace corrupted files" option next time I do a backup to double-check it.
 


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