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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  • repoman27 - Monday, September 15, 2014 - link

    Well, you clearly missed the point then. Promise already makes a whole line of 3.5-inch DAS offerings.

    The Pegasus2 M4 is very nearly the same in both size and weight to a stack of 4 bare 3.5-inch drives, yet it comes with 4 hot-swap drive bays, an internal 110 W PSU, a custom hardware RAID controller, and a 4-channel Thunderbolt 2 interface so you can daisy-chain up to 6 of them. The RoC is an 8-Port, 6Gb/s SAS / SATA chip with a PCIe 2.0 x8 back end, paired with 512 MB of DDR2-800 ECC SDRAM, 8 MB of external NAND, and a Lattice MachX02 PLD, all of which is arguably overkill for the intended application.

    The bottom line is that this "POS" extracts 100% of the potential of the drives it ships with, delivers peak performance beyond what is possible via USB 3.0, and does so as a single device that costs a grand. There are a *lot* of highly questionable Thunderbolt storage devices out there, but this really isn't one of them.
  • PeterBr - Sunday, May 3, 2015 - link

    Im new to this and have to build a drive for 4k video editing. Do you have a raid controller card in mind that you could point me to? I just bought this M4 last night and now Im considering returning for something more affordable.
  • CalaverasGrande - Friday, September 12, 2014 - link

    Not to be snarky, but really, what is the point of testing it at all if you can not beg borrow or steal a Mac? There may not be significant differences from your perspective. However the target audience for this product is Mac owners.

  • twotwotwo - Saturday, September 13, 2014 - link

    They do have Thunderbolt and aren't saturating the interface; I don't see the problem unless you would choose to buy or not based on the software.
  • WylyQuimby - Saturday, September 13, 2014 - link

    CalverasGrande has a point. Thunderbolt doesn't exactly have the best support on Windows. I have two TB drives. One is not recognized at all by Win8.1 and the other has to be plugged in before booting. For a good scientific test one should try to eliminate all systematic errors. TB devices are primarily purchased by Mac users, one should at least also test them on a Mac.
  • Osamede - Saturday, September 13, 2014 - link

    I must agree. It is great to see a Windows based analysis of this. Very useful. But........at the same time, the primary user base is on Mac OSX and it is a major omission to see a review that completely ignores that side the equation.

    Furthermore, there are other omissions, which are material to the type of user who would consider the product:
    - No discussion of drive height limits e.g. can I stick a 12 or 15mm height 2.5" drive in here
    - No discussion of noise/fan

    And the conclusion should have touched upon other similar products which use 2.5" drives and said something even brief about how this one here stacks up in performance, functionality and value compared to those.

    Overall this "review" was a bit on the shallow side and just not good enough IMO.
  • Death666Angel - Saturday, September 13, 2014 - link

    "- No discussion of drive height limits e.g. can I stick a 12 or 15mm height 2.5" drive in here
    - No discussion of noise/fan"
    First page specifically calls out 9.5mm drives. It does not mention 12.5mm or 15mm height in any way. I derive from that, that they aren't supported.
    Furthermore, in the conclusion, the article mentions the loud noise the fan makes.
  • Osamede - Saturday, September 13, 2014 - link

    Ok let me rephrase that. This is Anandtech - I expect more substance than this:

    "I did notice one irritating thing in the M4, however. The fan in the M4 makes a fairly loud noise even when the device is idling. Unfortunately I do not have a proper decibel meter to provide an objective measure of the noise."

    I mean just put out some numbers please. No numbers and there is no way one can compare this with the next product you review in two weeks. The objective and comparable approach is one major reason why people come here.

    Fair enough?
  • Gigaplex - Saturday, September 13, 2014 - link

    It stated fairly explicitly that they didn't have a meter to record numbers. Would you like them to make up some numbers?
  • Osamede - Sunday, September 14, 2014 - link

    Maybe your comprehension not very good - my point is they should have one and do document the numbers. Like I said, just not good enough.

    Worse yet is apologists for half-done "review".

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