Typically multi-bay external storage devices tend to utilize 3.5" drives due to the lower cost and higher capacities. The downside, however, is that 3.5" drives are physically larger and heavier, which makes a multi-bay enclosure rather difficult to move around on a regular basis. To fix this, Promise is offering a 4-bay 2.5" RAID solution called the M4.

Promise Pegasus2 Lineup
  M4 R4 R6 R8
Form Factor 4 x 2.5" 4 x 3.5" 6 x 3.5" 8 x 3.5"
Supported RAID Levels 0, 1, 5, 6, 10 0, 1, 5, 6, 10 0, 1, 5, 6, 10, 50 0, 1, 5, 6, 10, 50, 60
Connectivity 2x Thunderbolt 2 (20Gbps each)
Available Capacities 4TB 8TB 12TB & 18TB 24TB & 32TB
DImensions (HxWxL) 4.2" x 5.0" x 6.6" 7.5" x 9.6" x 7.3" 9.8" x 9.6" x 7.3" 12.2" x 9.6" x 7.3"
Weight 5.5lb / 2.9kg 15lb / 6.8kg 20.1lb / 9.1kg 24.2lb / 11kg

Aside from capacity, the M4 offers everything that the R4 does as you get hardware RAID 5 and two Thunderbolt 2 ports for daisy-chaining. The weight comes in at almost one third of the R4's weight and the dimensions are considerably smaller too, which makes the M4 a lot more portable than the rest of the Pegasus2 lineup. Sadly Thunderbolt 2's ten watts of power is not capable of powering the M4, so it is not a fully portable solution like regular external hard drives are.

The M4 is available for $999 in the Apple Online Store and the target market for the M4 and the whole Pegasus2 family is video professionals. Promise markets the M4 as a solution that offers portability for over an hour of uncompressed 4K footage. While there are arguably cheaper and larger external 3.5" hard drives around, the M4 provides redundancy via RAID 5, 6 and 10, which is more or less a must for professional video editing because data loss could end up being very expensive.

Our review unit shipped with four 1TB 5,400rpm Toshiba hard drives. These are 9.5mm i.e. two-platter drives, so we are not dealing with super high density here. Promise told us that they are not offering 4x1.5TB or 4x2TB configurations due to price sensitivity as $999 is quite expensive to begin with, although I am not sure if I agree because I could see video professionals paying more for increased capacity. In the end, 4TB is not that much if you deal with 4K video.

Fortunately Promise has made hard drive swaps convenient as pressing the button on the bay will free the lever, which you simply pull to get the drive out. The drives are attached to the bays by four standard hard drive screws, so any 2.5" drive will work. Officially Promise only guarantees compatibility with the Toshiba drive, although the user manual suggests that the drive does not have to be the same make and model.

Getting inside the M4 is fairly easy. There are a few screws that need to be removed until the top comes off and you end up having access to the PCB along with the rest of the components (PSU, fan, etc.). The RAID controller is covered by the heat sink, so I do not have a photo of it, but I was told that the silicon itself is from PMC with custom Promise firmware. A quick look at PMC's RAID controller lineup suggests that the silicon is the PM8011 SRC 8x6G, which is an 8-port SATA/SAS 6Gbps controller with a PCIe 2.0 x8 interface. 

Like many Thunderbolt devices, the M4 has two Thunderbolt 2 ports for daisy-chaining. The Thunderbolt controller is Intel's DSL5520 with two Thunderbolt 2 ports (i.e. four channels) and it connects to the RAID controller through a PCIe 2.0 x4 interface. Intel lists the bulk price as $9.95 on their ARK site and the TDP is 2.8W.

Test Setup

Unfortunately I do not have a Mac with Thunderbolt, so the results and analysis are limited to a Windows based system. Based on what we have talked with manufacturers, there is some difference in performance between Thunderbolt in Windows and OS X. A part of that comes from the fact that in PCs, the Thunderbolt controller is connected to the PCIe lanes from the PCH, whereas in Macs they come directly from the CPU. The Windows drivers are also not as good as the native OS X drivers, which I guess is not a surprise given that Apple has always been the biggest supporter of Thunderbolt. Either way, the results should represent performance under both OSs as long as we are not close to saturating the interface.

CPU Intel Core i7-4770K running at 3.3GHz (Turbo & EIST enabled, C-states disabled)
Motherboard ASUS Z87 Deluxe (BIOS 1707)
Chipset Intel Z87
Chipset Drivers Intel + Intel RST 12.9
Thunderbolt Adapter ASUS ThunderboltEX II/DUAL
Thunderbolt Drivers
Memory Corsair Vengeance DDR3-1866 2x8GB (9-10-9-27 2T)
Graphics Intel HD Graphics 4600
Graphics Drivers
Desktop Resolution 1920 x 1080
OS Windows 7 x64
The Pegasus2 M4: Software
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  • Zak - Friday, September 12, 2014 - link

    The 4xSSD performance is a little disappointing indeed. That would be #1 reason to get this enclosure. I get faster speeds, over 1GB/s reads, out of two SSDs on the onboard Intel RAID controller.
  • simonrichter - Friday, October 3, 2014 - link

    I agree, it is rather disappointing and it makes it an average storage devices that cannot match up to the top ones on the market (for example http://www.consumertop.com/best-computer-storage-g... ). But it should be interesting to see if they release an updated version of it.
  • jonb8305 - Wednesday, October 15, 2014 - link

    Promise has an SSD version of the m4 with way better performance than what was stated here.
  • bill.rookard - Friday, September 12, 2014 - link

    While I do somewhat see the use of a device like this, I'm not sure I see it really serving any real niche effectively.

    It's made to use small, portable drives, but it's not portable as it requires external power.
    It should be quick, but it's limited by the internals to about 1/4 of it's theoretical top speed.
    It uses the expensive Thunderbolt interface to be fast, but again, it's limited internally.
    It offers four drives, but keeps them to 2.5" drives without making the unit truly portable.
    It offers four drives for capacity, but then only offers 1TB drives.

    This device just seems like a whole series of compromises without really SERVING a niche effectively.
  • JohnMD1022 - Tuesday, September 16, 2014 - link

    Why not offer it as a bare box?
  • Drizzt321 - Friday, September 12, 2014 - link

    How about running the SSDs as single disks and using Windows RAID to check performance. Cut out the RAID controller, which them will leave us the SATA controller to test that to see if it's the RAID controller, or the SATA controller.

    And I agree, it's too bad it can't be bus-powered. Maybe when USB3.1 with Type-C connectors comes along it'd be able to power something like this. 100W is quite a bit of power, especially with 2.5" drives!
  • repoman27 - Sunday, September 14, 2014 - link

    If Kristian was correct in his guess that there's a PMC-Sierra PM8011 lurking under that heat sink, which is quite likely seeing as Promise uses that chip in several other products already, it's an RoC (RAID-on-Chip). So the SATA (actually SAS in this case) controller and the RAID controller aren't terribly separable.

    The performance scaling actually looks damn near perfect with the HDDs, and indicates that the RoC is actually a beast for the intended workload. I'm not sure why Kristian thought RAID 5 read performance would be higher. If you only stripe across three drives and write parity data to the 4th, it would be pretty challenging to read back faster than 3x the maximum a single drive can muster. In this case, the Pegasus2 M4 hit 355.5 MB/s vs. 120 MB/s for a single drive, or near as makes no difference 3x. And the 15% performance hit for sequential reads in RAID 10 doesn't seem too egregious, especially seeing as random reads went up by almost 17%.

    Kristian never mentioned what he was using for SSDs or if they were all identical. I'm guessing whatever he used, the RoC simply wasn't tuned for it. Although who knows, maybe the same test on a Mac would have yielded radically different results.

    100 W may be a lot for 4x 2.5-inch HDDs, but the Pegasus2 M4 appears to be packing a compact internal 110 W PSU from FSP. That's nuts!
  • HigherState - Friday, September 12, 2014 - link

    I know they say performance on win vs mac should be close, however those numbers are so dissapointing that its possible that its os driver related as well. Someones bound to have an old MBP to lend you for the test
  • repoman27 - Sunday, September 14, 2014 - link

    Well, the performance of the unit as it shipped isn't really disappointing at all. I mean, aside from not using something slightly peppier than the Toshiba drives, like maybe HGST Travelstar 7K1000's, what was Promise supposed to do?

    Clearly the SSD experiment was performed with a set of drives that had in no way been validated against Promise's firmware.
  • The_Assimilator - Friday, September 12, 2014 - link

    Or you could spend $700 on four 7200rpm 4TB 3.5" drives and a cheap RAID controller card, and build a RAID-10 setup that also wouldn't be portable, but would be fast and have 8 times the capacity of this POS.

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