[suhailpatel]

My rMBP updated just fine to 10.10.1 but when I went to update my sister's MBP with a 840 SSD and Trim Enabled I ran into the grey forbidden screen and safe mode yielded the 'Waiting for root device' error. This can be fixed by going into recovery mode (Command+R) on boot and running the following commands:

    rm -rf /Volumes/<10.10 Partition>/System/Library/Extensions/IOAHCIFamily.kext
    cp -r /System/Library/Extensions/IOAHCIFamily.kext/Volumes/<10.10 Partition>/System/Library/Extensions/IOAHCIFamily.kext
    touch /Volumes/<10.10 Partition>/System/Library/Extensions
    kextcache -u /Volumes/<10.10 Partition>

The update installed just fine after that, the commands disable TRIM and restore the original OSX kext which was replaced by TRIM Enabler

Commands Source: http://www.cindori.org/forums/topic/heads-up-osx-10-10-beta-...

[teamhappy]

I have the same SSD (Samsung 840 PRO) and had no issues at all. I highly recommend this script to enable TRIM: https://gist.github.com/return1/4058659

[kstrauser]

Be aware this script (and Trim Enabler) require you to turn off kext signature validation. This feature was added in 10.9 but it only raised warnings on missing or invalid signatures. It didn't actually prevent the kext loading. 10.10 now raises an exception whenever you load an unsigned or invalidly signed kext.

Disabling this check returns you to 10.9-level security and removes barrier to malware installing its own kernel modules.

[teamhappy]

Yeah, unfortunately there is no way to enable TRIM without turning off signature validation completely. Apple calls the feature kext developer mode. It would be nice to see them providing more fine grained control over which kexts are supposed to run in dev mode — or just enable TRIM for non-Apple SSDs in the first place.