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

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.

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.

About how long does each take?

Thank you, @ace and @Simon. Adam, I had not absorbed that bit from the Bombich article; thanks for quoting that.

Now, off to reformat the new disk.

There is that. But, OWC currently recommends DiskWarrior for the SoftRAID array I just purchased from them, and it did work to recover my 4-drive array three weeks in.

I’m trying to recall what Disk Utility said about the same array, but as I recall it was on the order of “huh, everything looks fine to me—wait, where did it go?” as it unmounted the array and wouldn’t mount it again.

As for your general advice, Adam, thank you. My current plan is to move the 2012 iMac to one side of my desk, install a 2019 27-inch with faster processor, and use the two of them in tandem. I’m toying with the idea of using the older machine as a Compressor processing station, which might work well or might run into version problems. Worth a try, as I’m generating enough minutes of 720p video every week to make a difference.

The current “see ya” list on a new machine would be the Adobe CS6 suite (which improbably still runs well under High Sierra), a few utilities, and some cruft that has come along from as far back as when OS X was introduced and I was running the whole thing on a Blue Dalmatian iMac that came forward from classic Mac days.

I appreciate the help @ace !

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Adam, articles like this always make me review my own backup strategy, which is currently based on a CrashPlan SMB cloud backup, and manual SuperDuper! clone drives, one of which is stored in our office, with more in a bank vault.

That last bit about manual clones is beginning to bother me. A lot.

From the article, it sounds as if your backup strategy relies on these three pillars:

  • Automated daily bootable clone
  • Local Time Machine backup
  • Cloud Backblaze backup

At this point, I’m considering the following changes:

  • Move from CrashPlan to Backblaze (a whole story in its own right…)
  • Getting a NAS device for local versioned backups
  • Attach an SSD drive for local cloned backups to our CalDigit docking station

Does that approach raise any red flags for you, Adam (or any other readers here :wink: )? Thanks for any suggestion on how to (further) improve what we have in place already.

Don’t have any personal experience with NAS devices, but many many others report issues with these, apparently some manufacturers more than others.

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The only issue is that NAS, not because I have any experience with it, but because I’m not sure I trust non-local solutions with Time Machine. It’s just not designed to work over a network—it has no client/server architecture—so interruptions are likely to cause corruption.

Dave Hamilton mentioned a workaround at MacTech Conference last year. If I remember right, the idea was that you could back up via Time Machine to a NAS using the btrfs filesystem, which allows regular snapshots, much like APFS. Then, if you had a Time Machine problem, you could revert the Time Machine backup to a previous snapshot to avoid any potential corruptions problems. I’ve never tested this, or even had a NAS, but it’s worth considering.

I do feel that bootable clones need to be on SSDs now, if you really think you’re going to boot from them and try to get work done.

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I create clones on hard drives. I don’t anticipate booting from them. Since my current desktop is using 2.5TB on a 3TB Fusion drive, creating multiple SSD clones would be expensive. When I have needed to fully recover a system in the SSD-Fusion drive age, I have always started with a clean install (either from an installation package or the Recovery mechanism) and then used the clone as a migration source.

Most of the space is occupied by my photo library and video files (mainly recorded shows from my TiVos or directly via Plex). A project I may finally complete during shelter-in-place is to move these libraries onto an external drive and develop a coherent backup strategy for that drive. After doing that, I can get out of the Fusion game.

5 posts were split to a new topic: Issues with the Time Capsule

For anyone wondering, my perception, unbacked by any measurement, is that copying a 500 MB folder with 11 items consistently takes less than a third of the time that it took to copy the same folder to an external spinning disk on the same USB hub.

I do have actual durations, as reported by SuperDuper!, for full backups to bootable clones. Typically, they take 2/3 the time, although the first backup to the T5 took 1/3 the time. (I welcome speculation on why the first backup was so much faster.)

If I assume your spinning disk does roughly 100 MB/s that would indicate you’re getting around 300+ MB/s. That’s not bad, but it’s still low compared to ~500 MB/s you see on even pretty inexpensive consumer grade SSDs. Almost as if there were an old SATA bridge in there (3 Gbps). Highly unlikely. I’m starting to wonder if UASP on Macs is a bigger deal than I thought. OTOH, IIRC a 2015 MBP’s USB3 peak bandwidth is 5 Gbps so maybe you’re just plain bus limited and the only way around that would be a newer MBP that supports 10 Gbps over USB-C (3.1 Gen 2).

5Gbps == 625MBps. Even if there is 20% lost to overhead, that would still be 500MBps.

In my last job, I was happy with Samsung T5s as external boot drives to perform support (i.e. temporary external boot drive) on dozens of Macs and for shuttling files. BlackMagic Disk Speed Test showed the T5 having the expected read and write performance but I didn’t obsess over numbers. I always expect a significant amount of time in transfers is for basically cataloging the new files, that there’s a lot more than creating a new name and pouring data into it.

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It’s very hard to find any USB3-attached drive on a Mac that will show real world throughput close to 500 MB/s. I’ve never understood the root cause for this, but I believe it’s safe to assume the overhead must be substantially more than 20%. In fact, the ~300 MB/s @Will_M mentioned I believe is much closer to what most people usually see over USB3 on Macs. Just an observation.