We hear from many Mac Pro owners asking about faster internal storage solutions. Trans International has just released a creative way to double the number of 6Gbps Solid State drives you can place in each drive bay with no loss in speed. They call it Double Decker.
The Double Decker sleds replace the factory sleds in the Mac Pro's drive bays. By facing the drive ports outward, each SSD can have its own data cable going to a fast 6Gbps internal host adapter like the Areca ARC-1882i or the ATTO ExpressSAS R608. The kit provides a power cable for each Double Decker sled that routes power to both drives from the Mac Pro's drive bay backplane. The internal mini-SAS to SATA data cables are included in the kit.
The graphs below show the large sequential transfer speeds attainable when various numbers of 6Gbps SSDs are mounted in the Double Decker and connected to a fast 6Gbps host bus adapter.
AJA System Test measures large sequential read and write speed (which emulates playback and capture of HD video). Settings used included 16GB File Size, 4096x2160 10-bit RGB Video Frame Size, file system cache Disabled. The results in the graph are AVERAGE SUSTAINED speeds, not just PEAK speeds. (HIGHEST number means FASTEST in megabytes per second.)
LEGEND of GRAPHS
ARC 1882 = Areca ARC-1882i Host Bus Adapter with two internal mini-SAS ports that support up to 8 drives. We tested using both AV Mode 1 and 3.
SSD*8 R0 av1 = Eight 6Gbps SSDs in a RAID 0 set with ARC-1882i's AV mode set to 1.
SSD*6 R0 av1 = Six 6Gbps SSDs in a RAID 0 set with ARC-1882i's AV mode set to 1.
SSD*8 R0 av3 = Eight 6Gbps SSDs in a RAID 0 set with ARC-1882i's AV mode set to 3.
SSD*6 R0 av3 = Six 6Gbps SSDs in a RAID 0 set with ARC-1882i's AV mode set to 3.
SSD*4 R0 av3 = Four 6Gbps SSDs in a RAID 0 set with ARC-1882i's AV mode set to 3.
SSD*8 R5 av3 = Eight 6Gbps SSDs in a RAID 5 set with ARC-1882i's AV mode set to 3.
SSD*6 R5 av3 = Six 6Gbps SSDs in a RAID 5 set with ARC-1882i's AV mode set to 3.
ATTO R644 = ATTO ExpressSAS R644 Host Bus Adapter with one internal mini-SAS port that supports up to four internal drives and one external mini-SAS port that supports another four drives. Though we tested with the R644, the ATTO ExpressSAS R608 with dual internal mini-SAS ports is preferred to support eight drives internally. The performance is the same for both models.
SSD*8 R0 = Eight 6Gbps SSDs in a RAID 0 set connected to the ATTO R644.
SSD*4 R0 = Four 6Gbps SSDs in a RAID 0 set connected to the ATTO R644.
Test Mule was a 2010 Mac Pro Westmere Hex-Core. SSDs were TransIntl SwiftSync 6Gbps 240GB (Synchronous).
INSIGHTS
The Double Decker literally doubles the number of drives that you can mount in the four Mac Pro internal drive bays. Of course, all eight would have to be 2.5" form factor, but for pro users that seek to attain the maximum transfer speeds, the 2.5" 6Gpbs SSDs are the 'weapon of choice.'
Though eight 6Gbps SSDs are capable of an aggregate speed of 4000MB/s, that transfer speed not possible through a single 8 lane host adapter. By tweaking the Advanced Settings and choosing AV Mode 1, the ARECA ARC-1882i was able to get our RAID 0 set of SSDs as high as 2700MB/s. However, using a slightly slower AV Mode 3, the transfer speeds were less erratic (as indicated by a flat line in our AJA System Test graph.) NOTE: Since the Mac Pro has PCIe 2.0 slots, be sure to disable the ARECA ARC-1882i's PCIe 3.0 mode. Failure to do so will slow your array.
Whether you use the ARECA, ATTO, or any other HBA, consult that company's tech support for best settings for your setup and use.
WHAT ABOUT SMALL RANDOM TRANSFER SPEEDS?
Intech's QuickBench was used test a mix of small random transfers from 4K to 1024K. The Areca ARC-1223-8i ranged from 718 to 808MB/s READ and from 443 to 825MB/s WRITE -- depending on the number of SSDs and type of RAID mode.
WHAT ABOUT HDDs INSTEAD of SSDs?
Don't forget that the Double Decker is designed for 2.5" drives. The fastest 2.5" hard disk drive (HDD) we have tested is the WD Black 750GB which tops out at 131MB/s. Eight of those in RAID 0 mode could reach 1000MB/s+. That compares well with four 3.5" 1TB Velociraptors in RAID 0 mode which would strain to reach 800MB/s. Yet, if maximum large sequential transfer speed and/or maximum random operations per second is your priority, the 6Gbps SSDs are the way to go.
THE KIT IS COMPLETE and FLEXIBLE
The Double Decker kit comes with all the data and power cables you need along with instructions for installation. You can buy it with or without 6Gbps SSDs and with or without a host adapter. There are two different kits: one for 2006 - 2008 Mac Pros and one for 2009 - 2012 Mac Pros.
