I made a comment on a blog post over at The Loop which I quite liked. I didn’t want it to just disappear so I thought I’d put a copy here:
Came across these Western Digital Black2 Dual Drive units the other day. What a cool idea I thought! Just the thing for a couple of laptop users here at work who prefer the speed of an SSD in their laptops but would like a bit of extra room for VM’s and the like.
So I ordered three – one for my work iMac as well. I’d recently upgraded the iMac with an older 256GB SSD – which was fine – though not a huge amount of space obviously.
The units arrived and I set about hooking it up to the iMac using the handy USB->laptop drive SATA cable that it came with.
Only the 120GB SSD drive portion appeared.
Digging a little further, I found that the unit is supported in Windows only – you need to install software in Windows to enable access to the 1TB disk in the Black2 Dual.
Once I’d finished ranting about how crap it was that a hard disk vendor would build a hard disk only for Windows, I had a think. There *must* be a way to make this work – surely! Just because they haven’t built this ‘enabler’ software for OSX surely doesn’t mean that it absolutely wouldn’t work.
So, I went to work getting it set up on a Windows laptop, figuring that I could unlock the disk in Windows & then pop it back in my iMac and configure a Fusion drive across the two disks.
Annoyingly – or cleverly I guess, depending on how you look at it – you cannot unlock the 1TB portion of the drive while it is connected via USB. It actually has to be resident inside the machine (or at least, connected to the SATA bus) to unlock.
This meant I had to image the existing SSD in the laptop onto this one – using the afore mentioned handy cable.
Once it was unlocked, I connected it up to the iMac and converted the partition table from MBR to GPT using the gdisk utility. Note that the 1TB portion shows up as a partition NOT a second hard disk I had suspected it might based on the reviews I’d read.
I removed all the partitions from the first 128GB of the disk and created an EFI partition then ran the Apple Recovery Disk Assistant tool to create a Recovery partition on the new disk.
Excitedly, I then used the directions here to create the Fusion drive.
diskutil cs create Fusion disk3s2 disk3s3
Unfortunately this resulted in a POSIX Input/Output error so it seemed like that was the end of the road.
Frustrated, I posted a brief report into a MacRumours forum in which I’d left a question.
Overnight, “Weaselboy” replied with a few further links to check which renewed my hope that it might work.
One in particular – this excellent (as usual) article from Anandtech described how the controller uses LBA to address the different areas of the disk. Here was the reason for my renewed hope.
Ok, I thought, let’s just wipe the whole thing in my iMac and create the partitions again.
So I did.
And, this time, it worked. Similar steps would mean this disk could be ‘enabled’ for use in a linux machine as well – it would work really well with / mounted to the SSD and /home on the 1TB mechanical portion.