I ran this update and it bricked my computer! My 3 TB fusion drive (128 GB SSD + 3TB 7200rpm drive) no longer works. I've been struggling with trying to get it back online for over a week now and running into all kinds of issues with the SSD.

Yup, I booted from another drive connected via USB. Still nothing. Diskutility is having no trouble with the 3 TB drive, just the 128 GB SSD.

Hmm, I'm not sure I understand the question but basically it was Disk Utility which identified the problem.

The updater said there was just a standard security update for OS X 10.10.4 > 10.10.5 plus updates for Safari, iTunes and maybe some others. After delaying them a day or two, I finally went ahead and attempted to install the updates through the standard App Store updater.

That's when things went awry. The update hung mid-way through and I was forced to do a hard reboot. That hard-reboot seemed to do something odd to the Fusion drive because the system would no longer boot.

When I finally was able to boot into recovery mode, I no longer saw my Fusion drive in the list, but rather two separate drives. I tried running disk repair on both, but the SSD kept giving errors.

I ordered a new SSD from Amazon today and will install it tonight. I was trying to avoid that as opening up the iMac requires a bit of effort, but I've tried everything possible I could find on the internet and nothing has worked.

@greg sahli -

Interesting, thanks for the article. Mine is a mid-2010 iMac 27" that did not come with a Fusion drive, but I added it manually later. So that article is very relevant. However, I have booted from a USB volume and tried repairing from there as well, but still having no luck. In fact, when I click on my SSD in the drive list, the Verify and Repair buttons are completely grayed out.

I've tried adding a partition, formatting, just about everything but nothing is working. It currently shows the SSD and HD as two different drives.

Maybe I should try a verify/repair using the diskutil command prompt if there is a way to do that and avoid the grayed out buttons.

I had previously tried a secureErase using the diskutil command and got the following result:

diskutil secureErase 0 /dev/disk0

Error: -69759: Securely erasing data to prevent recovery failed

Underlying error: 5: POSIX reports: Inputs/output error

No there was nothing about repairing the Fusion drive. It seems like in the whole ordeal the system lost all recollection that the two drives were a Fusion drive. I tried reinitializing them as Fusion drives following the standard process here but that failed too: http://www.macworld.com/article/2014011/how-to-make-your-own-fusion-drive.html

Last night I opened up the machine and replaced the SSD with a new one then reinstalled from my Time Machine backup overnight. Everything seems to be back to normal but I only did a quick check this morning before I left for work.

I investigated the old SSD and the connectors (both SATA and power) were damaged. It looked like the plastic around the connectors on the SSD side of the connection got brittle and broke (perhaps due to excessive heat cycling?) Pretty fluke thing if you ask me, but I guess it might not have been related to the software update after all.

I made sure to locate the new SSD a little further away from the heat source and a little closer to the conventional hard drive.

BTW, I mis-typed earlier and it was 10.9.5 update that originally caused the problem.