The Pegasus: Software

The Pegasus ships fully functional from the factory, but you'll need to do a couple of things to your Mac before the first Thunderbolt device on the market will just work. First, the Pegasus (or any TB device) will only work on a 2011 MacBook Pro or 2011 iMac as those are the only two systems on the market today with an integrated Thunderbolt controller. Apple is widely expected to introduce a new Mac Pro and maybe even a new MacBook Air with Thunderbolt support, but for now you need a 2011 MBP or iMac.

If you have one of those two systems you'll need two software updates. The first is the Mac Thunderbolt Firmware Update and the second is Mac OS X 10.6.8 (or later, Lion is supported). With both software updates installed, simply plug in a Thunderbolt cable and you'll be greeted with a Promise RAID icon on your desktop.

The bundled Promise Utility gives you full control over the Pegasus including reporting on drive/array health:

The major functions of the Promise Utility are pretty self explanatory. The Dashboard is the home screen of the application, it gives you a quick look at the current status of your drives/arrays (e.g. green for good, yellow for caution, red for major issue):

By default the Pegasus ships in a RAID-5 configuration with either 4 or 6 drives depending on whether you bought an R4 or R6 model. The RAID-5 array is configured with a 128KB stripe size and 512-byte sector size. This generally offers the best balance of redundancy and performance for most users, however if you'd like to delete it and start anew you can.

The wizard gives you one click array creation if you don't want to deal with adjusting things like stripe and sector sizes. There are varying levels of advanced array creation, or you can always go full manual.

You can choose any combination of drives in the Pegasus to be included in a disk array. From there you can partition the aforementioned disk array into any valid RAID array(s) you'd like. For example, you can choose to include all 6 drives in an array and from there create a 2TB RAID-0 and use the remaining space as a 6.4TB RAID-5. Alternatively, you can use five drives in an array and use one as a hot spare. Finally you can choose to only use some of the drives in an array and leave the remaining drives in pass-through mode, accessible outside of any RAID arrays.

Any drives you don't include in the drive array can be set as spares.

The table below shows you the options you have when creating a custom drive array on the Pegasus (I've highlighted the defaults):

Promise Pegasus Array Creation Options
Item Options
Stripe 64KB, 128KB, 256KB, 512KB, 1MB
Sector 512 Bytes, 1KB, 2KB, 4KB
Read Policy ReadCache, ReadAhead, No Cache
Write Policy WriteThru, WriteBack

All major configuration changes require that you type the word "confirm" before proceeding, a nice way to ensure you don't accidentally delete something.

The Promise Utility reports on both array and drive level events. It'll tell you basic things like whether or not your current array is healthy or down a drive. At the drive level you do get basic SMART reporting including temperature and health status. You also have the option of dumping an advanced SMART log to a text file which includes the drive vendor specific SMART attributes and their current, worst and threshold values:

In the utility's physical drive list you can locate any drive in the Pegasus array. Hitting the locate button will cause the corresponding identify LED to blink on the Pegasus.

Like any other array under OS X, you do have to manually eject any volumes before unplugging the Thunderbolt cable or powering down the Pegasus. Failing to do so will give you this all-too-familiar error:

The Thunderbolt Cable The Pegasus: Quirks


View All Comments

  • PrincessNybor - Tuesday, July 12, 2011 - link

    I'm actually looking forward to using Target Display Mode when I pick up my new 27" iMac this month (just holding out for Lion). My work computer is a 15" MacBook Pro with Thunderbolt, and while the display is good for a portable, I'd love access to a 27" display! Some of the applications I work with won't be installed on the iMac, since that will be a personal desktop and not a work machine. This is a good solution for others in my situation. Reply
  • osteopathic1 - Thursday, July 14, 2011 - link

    I just plugged in my old 23" Cinema Display DVI into a $6 minidisplay port/DVI adapter and it worked like a charm. Reply
  • wanlewanle - Tuesday, July 19, 2011 - link

    Come go and see, will not regret it Oh look
  • onebear - Saturday, September 24, 2011 - link

    Please see this discussions from Apple Support forum.

    It is not working with iMac 2011. And having many unsolve issues.
  • - Saturday, January 07, 2012 - link

    there are lots of known problems and promise won't answer or react on any of them.
    see a roundup of problems here:

    also there are other issues as reported in the apple forums:

    the only thing we can currently do is to boycott promise until the give an official statement and release a bugfix to support larger HDDs and address the issues/bugs (drive-ejecting bugs, etc.)
  • Rdubs - Friday, April 20, 2012 - link

    Anyone know if I can throw in 4x 4tb 3rd party drives into a R4?
    What's the limit? Can't find a list of what mfg' s hard drives play well
    with R4.

    Many thanks
  • frabber - Thursday, October 25, 2012 - link

    anybody know whether this is possible? with some kind of thunderbolt enabled motherboard? Reply
  • odedia - Monday, April 14, 2014 - link

    WD RED 4TB drives are pretty affordable now, for the price of the 8Tb R4, I can get a diskless R4 and 4 red drives, resulting in 16tb total. They question is, would the RED drives match the performance of the R4? They are 5400 rpm drives, though quite reliable (much better than a green drive). Reply
  • badex - Thursday, December 31, 2015 - link


    Have had my pegasus R4 for a couple of years. its been effective but i think i'd like to take a step up to using SSD drives. what SSD drives would you recommend for the pegasus R4?

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