Promise Pegasus R6 & Mac Thunderbolt Review
by Anand Lal Shimpi on July 8, 2011 2:01 AM ESTDisplayPort Passthrough
The Pegasus has two Thunderbolt ports. You can use the second port to daisy chain up to six Pegasus devices together, for up to 36 drives. With a single Pegasus in its default configuration able to hit over 5Gbps, you'd definitely run into bandwidth limitations with six of these things. But you could get by with two and not be limited by Thunderbolt.
There's another role that second Thunderbolt port can play: as a DisplayPort output. Remember both PCIe and DisplayPort are carried on a single Thunderbolt cable, the latter occupying half of the 40Gbps of total bandwidth available.
At the end of a Thunderbolt chain you can insert a miniDP display, currently the only option is the 27-inch LED Cinema Display but in theory other panels that accept a miniDP input could work as well.
I connected a 27-inch Cinema Display through the Pegasus without any problems. The Pegasus does have to be on for you to get video however, so if you ever have to shut down the Pegasus you do lose video to the Cinema Display.
Audio still works, so you'll see the Cinema Display as an audio device on your Mac:
The experience is pretty seamless overall.
I ran a quick test to see if I lost any bandwidth to the Pegasus with the 27-inch Cinema Display in the chain. I measured a slight performance drop (< 3%) in the best case scenario of four SF-2281 SSDs in a RAID-0 array on the Pegasus, but nothing substantial at all. Note that simply displaying an image at 60Hz on the 27-inch Cinema Display requires over 6.75Gbps of bandwidth (because of 8b/10b encoding), so a full Thunderbolt channel is necessary for DisplayPort (although admittedly it only needs to be unidirectional bandwidth).
| Thunderbolt PCIe + DP Bandwidth Test | ||||
| 2MB Sequential Write, QD16 | No DisplayPort Passthrough | 27-inch Cinema Display Connected | ||
| Promise Pegasus R6 (4 x SF-2281 SSDs, RAID-0) | 1002.7 MB/s | 988.2 MB/s | ||
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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.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.onebear - Saturday, September 24, 2011 - link
Please see this discussions from Apple Support forum.https://discussions.apple.com/thread/3181015
It is not working with iMac 2011. And having many unsolve issues.
nanofunk.net - Saturday, January 7, 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:
http://www.nanofunk.net/caution-with-promise-pegas...
also there are other issues as reported in the apple forums:
https://discussions.apple.com/thread/3181015?start...
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?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).badex - Thursday, December 31, 2015 - link
Hi,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?
thanks