Disk Utility version 15.0 which comes with El Capitan – and, perhaps more importantly, is available in its Recovery Drive – now has proper support for Fusion Drives and other CoreStorage Logical Volume Groups (LVGs). But Disk Utility is not always successful, and has a limited range of tools compared to third-party utilities.
So which disk repair and other utilities are claimed to be compatible with a Mac which is running its boot drive as a CoreStorage LVG?
Disk repair and maintenance
Alsoft’s DiskWarrior 5 is claimed to support “the latest Macs with Fusion drives”. No further information is provided about support for CoreStorage LVGs, and DiskWarrior appears to lack any features for addressing LVG issues.
Micromat’s TechTool Pro 8 is claimed to be compatible with El Capitan as well as Yosemite. Its documentation does not mention CoreStorage, LVGs, or Fusion Drives, though. Micromat claims that TechTool Pro 8 “officially supports Apple’s Fusion drive. All tests and tools can be used safely with one important caveat.” That caveat is, of course, that it will not attempt to defragment the SSD in a Fusion Drive, nor indeed any SSD, as defragmenting solid-state drives is both pointless and shortens their working lives. TechTool Pro 8 does not appear to provide any tools for dealing with LVGs.
Prosoft Engineeering’s Drive Genius 4 and Data Rescue 4.2 are claimed to be fully compatible with current Mac models running El Capitan: “Drive Genius 4 fully supports the latest Apple technologies, including Fusion and FileVault2 drives.” Prosoft also cautions that defragmentation is not available for SSDs, including those in Fusion Drives, and does not appear to provide any tools for addressing LVG issues.
Disk copying or cloning
Bombich Software’s Carbon Copy Cloner 4 is claimed to be fully compatible with Fusion Drives and CoreStorage LVGs, but these complicate matters, particularly with respect to the Recovery partition. Full details are given here. For instance, this states that “CCC cannot create a Recovery HD volume on a Fusion or FileVault-protected volume, therefore CCC will never allow you to remove the Recovery HD volume that is associated with a Fusion or FileVault-protected volume.”
Shirt Pocket’s SuperDuper 2.8 is claimed to be “compatible with El Capitan.” Although no further details are given in the documentation or on the vendor’s website, details of the sorts of manoeuvres required to deal with LVGs are given by Peter Upfold, in the context of making an encrypted bootable backup using SuperDuper and lots of shell commands.
SoftRAID 5.1 is claimed to be “fully compatible” with El Capitan. However it specifically does not support the use of Fusion Drives, but does support SSDs. You can of course use a SoftRAID-driven RAID with a Mac which runs from a Fusion Drive.
Current disk tuning, repair, and recovery tools – other than Disk Utility – all work at the HFS+ level, and thus function normally with Fusion Drives and other CoreStorage LVGs. However as they do not provide tools for dealing with LVGs, if you suffer a problem with a Fusion Drive or LVG you will probably find yourself having to address any CoreStorage issues using Disk Utility and/or the command shell.
It is about time that third-party tools caught up with Disk Utility and
The use of cloning tools such as CCC and SuperDuper is limited by CoreStorage: you can no longer clone a complete bootable disk back to a Fusion Drive or LVG. Gone are the days when you could clone your internal drive to an external one, fix the internal disk, and clone everything back again.
So whilst your Fusion Drive may be making El Capitan run sweetly, for the time being it makes any sort of disk problem that much more complicated.