An External SSD to Boot My iMac

I'm using a Mid 2011 27" iMac at work. When I ordered it back in May of last year, the SSD option would've prolonged the delivery estimate by a whopping 4 weeks, which, for an impatient person, is a hefty trade-off, so I passed and ordered the internal 1TB SATA drive only.

But, as they say, once you went SSD somewhere, you're not going back.

While the machine was definitely fast and usable for the first couple of months, I missed the speed of an SSD soon enough when switching back and forth between my MacBook Air and the iMac at work, especially at boot time and sleep/wake. So I certainly was more than happy when LaCie announced in June that their Little Big Disk would ship with Thunderbolt-connectivity and an SSD inside. This would allow me to get back onto the sacred SSD path while not making me jump through a plethora of suction-cup laden hoops in order to replace the internal drive of my iMac with an aftermarket SSD. (And that's not even guaranteed to work in the first place, after all.)

Not being located in the land of milk and honey, for the longest time the Thunderbolt version of the Little Big Disk was available in Germany only in its 1TB and 2TB SATA configurations. Finally, though, the 240 GB SSD version went on sale in recent weeks and I got my copy a couple of days ago.

Despite being advertised as a 240GB disk, it actually consists of a striped set of two 120GB SSD drives inside its aluminum chassis. It does not have any on-board RAID intelligence though and simply resorts to Mac OS X's built-in software RAID functionality. Using Disk Utility, you can reconfigure the Little Big Disk to work as a mirrored set (RAID-1) instead, giving you only 120GB of capacity. Or you can opt to simply use the two drives as individual disks.

To connect the chassis to your Mac, you'll need to bring your own Thunderbolt cable, since LaCie does not include any cables with its boxes¹. Also of note is the fact that the Little Big Disk needs its own power brick, as, apparently, the 10W of supplied bus power through the Thunderbolt bus is not sufficient to power it².

Of course I was curious about the performance of the cute little box, even though the theoretical speeds of 20Gbit/s of the Thunderbolt bus would hardly be the limiting factor. When I had everything wired up to one of the two Thunderbolt ports of my iMac, I fired up the Black Magic Disk Speed Test and got quite satisfactory results of 250MB/s write speed and 480MB/s read speed, respectively. My Late 2010 MacBook Air, by comparison, clocks in at roughly 100MB/s write and 140MB/s read speed on its internal SSD.

Quite happy with the results I fired up SuperDuper and cloned my internal SATA boot drive onto the Little Big Disk, the former certainly being the limiting factor in this operation.

After setting the external SSD as the new boot drive I rebooted my iMac and then designated the internal SATA drive to be the Time Machine backup drive. At 1TB capacity, it's giving me more than enough room to store both a significant Time Machine history as well as my iTunes library files on it³.

Given the Time Machine backups I kept my setup on the default stripe-set configuration, giving me the full 240GB of SSD capacity.

At this point, applications launch with a single "bounce" in the Dock, running test suites of my various Rails and Python projects are crazy fast, and, despite the speed increase, my workplace didn't get any noisier due to the almost complete silence of the Little Big Disk.

Conclusion

As an aftermarket option to speed up an existing system I can highly recommend the Little Big Disk Thunderbolt 240GB SSD. While it does have its price tag ($900 for the disk and $50 for the cable), adding a 256GB SSD built-to-order option to a new iMac (in addition to the default internal 1TB drive) also sets you back $600, so it's not that much more. Plus, you could theoretically boot any Thunderbolt-equipped Mac from the external SSD should your iMac give you hardware trouble one day.