Six Lessons Learned from Dealing with an iMac's Dead SSD

I also installed an SSD kit a year ago in my 2014 27" iMac 5K. Prior to that I used a Samsung T5 as my boot drive for about six months and things felt faster, but nothing compared to what I’m realizing now with the internal SSD.

There are times where I crave a faster iMac, but Python, shell scripts, and Affinity Designer are just fine with the old gal.

I’m lucky to also use a 13" MacBook Pro from work and use Jump Desktop to connect to it from the iMac since I run Windows via Parallels Desktop sometimes.

I honestly feel my iMac has much more value than what I would get if I sold it. The display is pretty cool. I also use Parallels Tools with Switch Resolution in the menu bar and sometimes take advantage of the full 5K when my eyesight is doing well.

By the way, I’m using an older 2010 iMac 27" in Target Display Mode as my second display and that’s a nice setup. :slight_smile:

I have never seen this mentioned there either, despite using some of the latest USB3 docks that I know offer support for UASP.

I have been told that in order to really check you have to look under Software > Extensions and check which kernel extension is actually loaded, IOUSBAttachedSCSI or IOUSBMasStorageDriver. If the former is loaded you are using it, if only the latter is loaded you are defaulting back to the old USB MSC. I have only seen the latter on this 2013 MBP so I’m assuming its USB3 is simply too old to support it.

Adam, I also thank you for the detailed write up. Articles like this (and all the comments) are one of the primary reasons I subscribe to Tidbits. And I agree with Doug Hogg – this kept me riveted in my seat to the end.
Some of my interest was generated by trying to update my 2013 MacBook Air to High Sierra. (yeah - I don’t keep up with all the new stuff :slight_smile: I was forced into an upgrade after installing a new application which could not run under Sierra. And the Mac App Store wasn’t helpful as it was forcing me to jump straight to Catalina. I did not want that because of some 32-bit apps that would be left behind.

It was quite an effort to find a link to the correct Apple installer. Just wish I’d seen Roland Mansson’s post with all the handy-dandy links right there. Gotta keep a copy of that one! Will likely move on to Mojave now that he has provided the article with its link to the installer.

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A quick web search finds this Apple discussion thread from 2014. The procedure described is:

  • Run the ioreg command to get the entire USB device tree, capturing its output to a file
  • Look for lines with devices of class IOUSBDevice and IOUSBAttachedSCSI. These are your UASP devices
  • Non-UASP storage devices will be of the IOUSBMassStorageClass

(The original version of this post mentioned an iousb command. That was a typo. Sorry.)

Thanks, @Simon. I got all excited because IOUSBAttachedSCSI was listed under extensions, then I reread your post and checked if it was loaded. It was not. I don’t suppose there is a way to tell the Mac to load IOUSBAttachedSCSI rather than IOUSBMasStorageDriver (which was listed as loaded)?

Thanks, @Shamino. I thought I was smart enough to do this, but I wasn’t. Terminal disavowed all knowledge of an iousb and I didn’t know where else to run it. Do you have a hint for me? (It probably doesn’t matter, since I assume the Software > Extensions result is conclusive, but I like to learn—even though I expect I’ll promptly forget what I learned.)

And another question, for anyone. After getting a System Report from About This Mac, clicking on Software > Extensions, and locating IOUSBAttachedSCSI, I thought to myself, “I’ll print this so I’ll have it later.” But in the Print dialog box available from System Information, I could find no way to print the selection or choose anything other than a page range for printing. Since the report was 102 pages long, it seemed like it would be tedious to find what I wanted, and I gave up. Did I miss some easy way to print just the IOUSBAttachedSCSI section (or any other section or group of sections)?

Also, repeating a question from my earlier post, how much of a performance hit would I suffer by using the Samsung T5 disk without IOUSBAttachedSCSI?

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Na, it wil load the kext if it can do it. If it isn’t loaded either the Mac or the bridge or the disk doesn’t support it (the former being the most likely).

The tip @Shamino gave you is just the command line equivalent. Its output is what Sys Profiler is displaying for you in a GUI. If you want to use the CLI, you have to do it using the command (I think he made a typo here)
ioreg
which will dump a whole bunch of stuff so most people usually send it to file as in
ioreg > ~/Desktop/ioreg.txt.
However, that’s a huge can of worms so it’s probably easiest to narrow down using something like
ioreg | grep -i iousb
or
ioreg | grep -i iousb > ~/Desktop/ioreg.txt
if you prefer a text file as output.
That should contain only the relevant parts of the output. You will see that MassStorageDriver shows up instead of USBAttachedSCSI, like what you got from Sys Profiler. If your (or my) Mac supported it, we’d be seeing the other kext listed because that gets loaded for a UASP connection.

To answer your final question, when using UASP with an SSD instead of MSC you should see considerable read/write improvements, but of course you’ll always be limited to below the SATA3 bandwidth of 6 Gbps (which is why Gen2 can still make sense over Gen1 when using USB3 bridges).

By the way, is anybody seeing arrows at the top of this post indicating it was a direct reply to @Will_M? Or does anybody else see any indication at @Will_M’s post that it was replied to below? There used to be such indication on this board, but now at least sporadically, I’m not seeing them on some posts. Is this just me or is it some kind of bug in the latest Discourse version Adam has applied?

Sorry. Typo. The command is ioreg. I’ll have to go edit my post now…

As @Simon wrote, the system profiler shows you the same output. But when you run it from a command line, you can redirect the output to a text file:

cd ~/Destkop
ioreg > foo.txt

Then you can load the file into your favorite text editor or word processor and use its features to search for keywords like IOUSBAttachedSCSI

It appears that those back-arrow links only appear when all of the following conditions exist:

  • The post does not immediately follow the one it is in reply to
  • The post does not quote any text from the post it is in reply to

Bug or feature? That answer is beyond my pay grade. :slight_smile:

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I’ve been confused about this as well. Weather it’s a bug or not, maybe Discourse should consider upgrading it.

Thanks, @Shamino. Makes sense I guess.

Been there done that and experienced worse trouble. Quite an adventure for sure.

I am surprised you didn’t just use the MacBook Air with Catalina to download the Mojave installer and then burn it to a USB 8GB flash drive and boot that on the iMac then run a Time Machine restore or cleanly install Mojave on the external Samsung T5. Also booting from a flash drive would be a cleaner way to run disk checks on the internal drive as it’s entirely not in use.

In Terminal:

sudo softwareupdate --fetch-full-installer --full-installer-version 10.14.6

Then (where MyVolume = USB Flash Disk Name):

sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

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Thanks for the article. I feel your pain. I recently had an issue with the SSD in my 2010 MacBook Pro. It started having issues shortly after a security update and at first I chalked it up to a corrupted system install.

After servers attempts to reinstall I dug deeper and found signs the SSD was failing. In the end I was fortunate as I had long ago replaced the DVD drive with a second SSD and was able to do a clean install on that drive and then restore my files from a backup.

Restoring all my settings and preferences in a clean install also cleared up a lot of other minor issues, but it was definitely a time consuming process :smirk:

Good idea! I think it basically fell into the category of too much extra work once it became clear the installer I had wasn’t going to be a help. Plus, I don’t know if I have an 8 GB USB flash drive—I have 20 or 30 of them around, but because I never buy them, they’re all really random sizes.

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The physical disk uppermost level is Fusion Drive and selecting this does not offer the erase option. I’ve been trying to recreate my Fusion Drive now for several months including advice from Adam and the gang but all efforts have failed I now run off an external SSD.

Based on the comments in this thread, I think it makes sense for me to format an SSD external drive as HFS+, since I expect to make bootable backups (of Mojave, for the foreseeable future) on it. (Also, Disk Utility does not offer APFS as an option.) I think this means I want to select GUID Partition Map. Is this correct? Thanks.

Why as HFS+? If you’re ever going to be booting from it with Mojave, APFS would make more sense.

The main benefits of HFS+ right now are better performance on external hard drives (not SSDs) and the requirement that Time Machine drives use HFS+.

Do you use or plan to use any disk diagnostic software like DriveDx? I’ve read that these can prevent disasters.

Is it possible SSDs are less reliable than mechanical drives?

I thought I had found at least two and maybe three discussions in favor of HFS+ earlier in this thread, but now my hurried search has turned up only one definite statement.

Less definite, but also nudging me in favor of HFS+, were these.

I’m not sure why I assumed, when I read that last snippet, that you were running APFS.

Anyway, in answer to @countermoon’s question, I do not use any non-Apple diagnostic software and I have no definite plans to do so, but it’s always a possibility.

On a different issue, I said that Disk Utility didn’t offer APFS as an option in the Format dropdown menu when I did a test run. I now see that APFS is an option if I select GUID Partition Map.

So, @ace, based on your query that started this lengthy post, it sounds like I misunderstood about APFS and that is the format scheme I should use, in which case GUID Partition Map is the partition scheme I should use. Yes? Thanks.

In this day and age, you definitely want GUID unless perhaps you still need to be able to boot a PPC Mac from that disk.

Yep, I’d recommend using APFS plus GUID for an SSD.

Of the notes you quoted, the main one that’s of real concern is the slowdowns at startup with a Samsung T5 formatted as APFS. However, the final line of Bombich’s page makes it clear this isn’t optional:

Another note: HFS+ is not a suitable format for a production startup disk. It’s fine to format your Mojave backup disk as HFS+, but if you’re using your Samsung T5 as a production startup device, you won’t be able to apply system updates to that volume as long as it is formatted as HFS+.

While I feel badly about what APFS has meant for DiskWarrior, I firmly believe at this point in time that no disk repair software other than Disk Utility is worthwhile for everyday users. It’s just so much more sensible to maintain good backups and, in the case of disk problems that Disk Utility can’t fix, to erase and restore. That way you’re never wondering if the repair software might have made a mistake or not known about something that Apple changed in a subtle update, etc. (I say “everyday users” because consultants or techs who fix other people’s drives definitely should be using disk repair software as necessary to get drives to be usable to the point where they can be backed up.)

I’ve now been running from the external T5 for a few weeks, and it has performed well. The startup and shutdown times might be slower, but I restart so infrequently that I haven’t really noticed.

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