Why won’t my SanDisk Extreme SSDs mount on MacBook Pro after macOS 15.5 update?

There are multiple class action suits against sandisk for intermittent failures due to hardware faults in their extreme pro drives.

I personally had mine fail like this over a year ago, unrelated to any software update, with footage from a days shoot, and a major client issue. (Most was recovered from original cards, but my bad).

upon reformatting, I cautiously used the drives only for it to happen again. Both were when moving files between different Macs.

It was not appearing in disk utility. However, days later, trying on a different Mac it did reappear and system utility repair recovered it.

I gather the issue is also related to heat and soldering issues, and there have been firmware updates that were supposed to help, but I certainly don’t trust it with any data not securely backed up.

SSD drives gave me the impression at first if being much more reliable than mechanical traditional hard drives, but that is not the case. They still fail, in different ways.

I would try to make sure your drives are cool or even cold, then one at a time, try connecting them to different Macs and disk utility. If they appear there, use repair, and immediately move all your files to another drive. There is a good chance some combination will allow them to reappear.

Do not re-format the drives. A last resort would be to ask sandisk to recover your data. As they are under pressure (google sandisk extreme pro failure lawsuit) they should oblige, and I suspect they have tools to recover data.

Lastly, and I suspect you know this now, buy a $200 or less large external harddrive and always backup critical data. It takes too many people (including me) to learn this the hard personal way.

svdrifter wrote:

I am now totally convinced that the issue was absoulutely and unequivicably due to issues with the macOS 15.5 update and not the drives themselves!

It seems that your experience indicates the opposite -- as all your failed drives are from the same family of drives made by the same manufacturer. We have over 1,000 Macs where I work and nearly all have one or more SSDs attached (for backups or other storage). We are also all mandated to be on 15.5 and I have not heard of any of these drives failing. But none are Sandisk, we have a limited number of manufacturers' drives to obtain from the employer's "catalog," and they include a variety of other makes but not those Sandisk SSDs.

Not a statistical sample, but I have WD, OWC, and Samsung SSDs in use on my personal computers running 15.5, and no issues seen. I even have one WD SSD, and WD and Sandisk are now the same vendor, but mine works fine and its serial number is "not affected" according to Sandisk's web site.

Given that Sandisk SSDs have had these issues in the past, I say where there is smoke there may be fire and suspect Sandisk drives manufactured in a certain time frame are likely flawed and not compatible with 15.5.

A fair amount of time later, something changed such that this drive ("SanDisk3") indeed did mount

Just recently, "SanDisk2" (APFS) has now been mounted

I have now even been able to mount "SanDisk1" and display its contents... sort of. By "sort of", I mean that the drive will mount and display file structure (the folders and the data sizes of each), but will still not display the individual filenames and their size. If I command-double-click a folder, it opens as an empty folder with the name displayed in the header.

The reason the drives take a long time to mount is that they are corrupted and the MacOS automatically runs FSCK on a drive when it appears to be corrupted. This can take a long time, many minutes. When it completes, the drive does mount, but if it could not be repaired it will still exhibit problems (like the ones you see).

I'm now confident that the OS update is at fault and not the drives.

I don't think that is likely because many millions of users who have external drives would have seen similar thing and that has not happened.

, I guess I'm going need to purchase a massive drive to back these up. Any suggestions? "OldToad" recommended SSDs from OWC (MacSales.com)

I don't see how you will be able to back them up because they are corrupted and not mounting properly. OWC products are excellent, in my experience.

Notice in the screenshot that the "SanDisk1" (on the left) shows all subfolders and their sizes, but NOT the files themselves, even tho the foders and subfolders are opened.

That is a sign that the drive has failed, and/or is corrupted. Such a drive is not usable. If Disk Utility First Aid cannot repair it, the best you can do is use other products to try to recover data or go to a (expensive) service for that. But this tends to be a lost cause for SSDs. These drives will not "get better" over time, unfortunately.

I don't know what to suggest but maybe change to a different model of external SSD going forward?

svdrifter wrote:

It's bad enough to lose a thousand dollars worth of drives, but I've also lost TWO YEARS of work! I've seen a couple of others on this site, but with smaller capacity drives and they only had one. I realize the importance and backing up important data, and I do so with my laptops.

That's a shame but it's why it is essential to back up everything of value.

Again, I appreciate your feedback. I will contact SanDisk to see if they can recover the data and I'll contact Apple Support for suggestions.

I believe this is an issue specific to this make and model of SSD. I actually have one myself and it is working but I did check on the Sandisk web site and enter my serial number, it returned with "your product is not affected."

(https://support-en.sandisk.com/app/firmwareupdate?#snlookupform)

After every update to MacOS, there are a small number of reports of disks not mounting or visible at all. You can check back in Apple Discussions for earlier MacOS versions. Same thing happens on PCs, a very small fraction of them. But because it is not widespread and here seems to impact a specific unit/model, I think it is on the Sandisk side.

If you are using a hub, try a direct connection and try a new cable. I have noticed "quirks" when using some drives and hubs. I use a OWC hub/dock at work, it has two Apricorn secure drives connected. If I dismount those drives and go away, then return with laptop and reconnect to the hub, one of them mounts immediately, the other doesn't seem to exist. If I physically disconnect it from the hub and reconnect, it shows up immediately like the other. And I have never seen any disk corruption with those drives. Why this behavior? The two drives are different models, the older model has this "quirk," maybe there is some interaction with the hub, although that OWC hub is top of the line and a very respected and reliable model.

If you are seeing actual drive corruption (I guess you can't see the drive at all now) then since it is an SSD, it may be unrecoverable, unfortunately.

Although you report that this happened after updating to 15.5, in fact dating back to 2023 there have been reports of problems with these drives. They typically show up in the video or photography community of users. Here is one:

https://arstechnica.com/gadgets/2023/05/sandisk-extreme-ssds-keep-abruptly-failing-firmware-fix-for-only-some-promised/

There was a firmware update.

https://support-en.sandisk.com/app/firmwareupdate

Not sure if this is applicable to your models.

svdrifter wrote:

I have no doubt that "the issue is disk corruption" and that "something wrong with the drives".

You should try running Disk Utility First Aid on the physical drive to check the partition table, then on the hidden Container (for drives using APFS). Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drive & hidden Containers appear on the left pane of Disk Utility. Even if the First Aid summary says everything is "Ok", click "Show Details" and scroll through the report to see if there are any unfixed errors listed. If there are errors, try running First Aid again. If after a couple attempts the errors remain, then they cannot be fixed.

Perhaps you can try using the command line to manually mount those drives as read-only without any file system verification scan.

If this had only happened to one of my three 4TB drives, I would not suspect the macOS update as the issue. But since it happened to all three drives at the same time, immediately after the macOS 15.5 update, I think there's little question that Apple's update was the cause!

Since all three SSDs are identical, it is hard to say for sure. It could be a bug with those SSDs as well. Or a bit of blame for both parties.

I would recommend physically disconnecting the drives prior to any system updates or upgrades to minimize accidental issues from occurring to them. Plus if they don't work afterwards, then you know there is some sort of compatibility issue between the OS update & those drives and not anything else. Over the years I have seen a lot of things happen to mounted external volumes due to OS updates, app updates, or software installs.

FYI, SSDs are susceptible to "corruption" due to power related issues. Plus SSDs can & usually fail at any time without any warning signs. Don't use an SSD without a good backup. Also the data on an SSD can degrade over time if the SSD is not connected to power. I've seen reports of SSDs becoming corrupt in as little as one year of sitting on the shelf unused because the NAND memory chips on an SSD need a periodic refresh once in a while so SSDs are not good for long term storage of backups sitting on a shelf.

You can try checking the health of those SSDs by running DriveDx (free trial period). You will need to install a special USB driver in order to access the health information of the external drives. Post the complete DriveDx text report for each SSD so I can examine it for possible clues (not all "warnings" or "failing" notices for an SSD are a problem....a manual interpretation is required). Post the report using the "Additional Text" icon that looks like a piece of paper on the forum editing window toolbar. Since you have a second older Mac, it may be best to use DriveDx there since I just saw a user report an odd bug that occurred while the DriveDx app was open on macOS 15.x Sequoia.

Open Activity Monitor in Utilities, View>All Processes, sort on Name, see if fsck is running, if so force quit it.

Continued....

It's bad enough to lose a thousand dollars worth of drives, but I've also lost TWO YEARS of work! I've seen a couple of others on this site, but with smaller capacity drives and they only had one. I realize the importance and backing up important data, and I do so with my laptops. But I'm made of money, and having developed on Apple products exclusively since the mid-80s, I can only recall once or twice that I've lost data (and MUCH less of it).

You need a backup strategy. Data loss is guaranteed if you don't have good backups, it is just a matter of time. I know it is difficult & expensive to backup large amounts of data, but that is just part of the job.

I would also suggest that you may want to consider a change to your setup. Perhaps a NAS would work out better for you. Many NAS systems utilize RAID 1/5/6 so that you can keep your data online 24/7 even in the event of a drive failure giving you time to replace the failed drive & rebuild the RAID array....hopefully before the next drive fails & you lose all the data. RAID is not a backup in & of itself, although a backup drive may utilize RAID.

You could backup the data on the NAS to a USB3/4 or Thunderbolt3/4 drive connected directly to the NAS. Of course you would still need another drive to perform backups of your computer and any other external media (including the cloud) which contains important & unique data.

With that much critical data, having a second backup option would be recommended....perhaps one where you can store the second backup off site somewhere as well. Cloud backup services could be a good secondary option, but restoring such large amounts of data is typically extremely slow unless they place the backup onto a drive & mail it back to you. You also have to worry about unauthorized access unless you encrypt the data & hold the encryption keys and subscription fees. And online services can change or cancel contracts at a whim. Having a second Hard Drive backup or an LTO tape backup could be another option to keep backups local. It is easy to keep a 2nd Hard Drive or LTO tape at another remote location as well for longer term backups.

By keeping the majority of the data on the network share you do isolate it a bit more from the Mac itself since you are only dealing with a mounted remote volume.

I'm sure others may have other ideas & suggestions as well for backup strategies.

Edit: I would also suggest disconnecting all other external devices in case one of them is causing a problem. This includes connecting just one SSD as well.

I have also seen some reports where an external drive may work better when connected to a USB3 hub instead of directly to the computer. Usually it is the other way around, but not always.

Also, try booting into Safe Mode to see if it makes any difference access the SSD.

svdrifter wrote:

I recently updated my macBook Pro 16 wirh the 15.5 release. Typically, I do not do these updates immediately, but wait for others to find the issues. This time, it caught me off guard and I just accepted the update. BIG MISTAKE!

There appear to be several issues on my internal drive. But the most critical oribken is with regard to my external SSDs. I have three SanDsk 4TB Extreme SSD drives, each containing about 3.5 TB of critical (and irreplaceable) data. Following the update, NONE of the three SSD drivies will mount! Other [conventional] drives do seem to mount OK, but these three are my most important drives.

I waited for a while to see if others had similar problems before posting this issue, but I have not seen any posts suggesting as much.

Any suggestions?

see if there is anything here—

https://support-en.sandisk.com/app/firmwareupdate

Glad you are on the road to recovery, but I can assure you that this is a drive problem and not Apple's issue. It is exactly the behaviors I had with my drive and that hundreds of others have reported on Reddit and in the lawsuits. My issues of disappearing completely both happened after the movement from one machine to another to another machine of different vintage and OS. This sensitivity is some flaw in their product. Search Reddit for some more info about them. I've used Sandisk SD cards on my video & still cams since they started using them, but this great featured new product has a peculiarity with changed systems. That's why these 3 dropped, and other drives haven't. Although my buggy ssd survived the upgrade, I still chose to use a traditional portable external to bring some large data to an associate's today, even though it would have been a lot more convenient....

I'd suggest an affordable traditional external hard drive 12 - 18TB. These little drives aren't meant for sustained editing use anyway.

Are your SanDisk Extreme SSD drives formatted APFS? ExFAT?