Adaptec RAID 6805
Chip manufacturer PMC-Sierra introduced its "Adaptec by PMC" Series 6 RAID controller family in late 2010. The Series 6 controller cards are based on the dual-core ROC (RAID On Chip) SRC 8x6G controller, which supports 512 MB cache and up to 6 Gb/s per SAS port. There are three low-profile models available: Adaptec RAID 6405 (four internal ports, about $320), Adaptec RAID 6445 (four internal and four external ports, about $475), and our test subject, the $460 Adaptec RAID 6805, which features eight internal ports.
All models support JBOD as well as RAID levels 0, 1, 1E, 5, 5EE, 6, 10, 50, and 60.
Connected to the host system with its x8 PCI Express 2.0 interface, the Adaptec RAID 6805 supports up to 256 devices via SAS expanders. According to manufacturer specs, the sustained data transfer rate to the host computer can reach up to 2 GB/s, while the peak performance can reach 4.8 GB/s on the aggregated SAS ports and 4.0 GB/s on the PCI Express interface – the latter is the maximum theoretical transfer rate of a PCI Express 2.0 x8 bus.
Maintenance-Free ZMCP
Our test sample came with Adaptec's Flash Module 600, which implements Zero Maintenance Cache Protection (ZMCP) and renders obsolete the traditional Battery Backup Unit (BBU). The ZMCP module is a circuit board with a 4 GB NAND flash chip, used to back up the contents of the controller's cache in the event of a power failure.
Because the copy operation from cache to flash is very fast, Adaptec's able to use a capacitor to keep power flowing, rather than a battery. The capacitor's advantage is that it should last as long as the card, whereas battery backup has to be replaced every couple of years. Additionally, once cached in flash memory, saved data lasts for years if need be. In comparison, you generally get about three days of data retention from a battery backup unit before the cached information is lost, forcing you to move fast on recovery. As the ZMCP's name suggests, it's a zero-maintenance solution, able to withstand extended power loss.
Performance
The Adaptec RAID 6805 in RAID 0 mode falls short of its competitors in our streaming read/write tests. Then again, RAID 0 probably isn't a typical use case for a business looking at data protection (though it could be for a workstation user rendering video). Sequential reads clock in at 640 MB/s and sequential writes are almost identical at 680 MB/s. In those two metrics, LSI's MegaRAID 9265-8i tops the charts. Adaptec's RAID 6805 performs better in the RAID 5, 6, and 10 tests, but isn't really a first-place finisher. In an SSD-only setup, the Adaptec controller reaches up to 530 MB/s, but is outperformed by the Areca and LSI controllers.
Adaptec's card automatically recognizes what it calls a Hybrid RAID configuration, which consists of mixed hard drives and SSDs, offering RAID levels 1 and 10 in that configuration, and claiming to outperform the competition through special read/write algorithms. This consists of directing the read operations exclusively to the SSDs, while write operations obviously have to be passed on to both the disk drives and SSDs. Thus, read performance should come close to an SSD-only setup, while write performance should be no worse than an all-disk-based setup.
Our tests results don't quite reflect such a theoretical situation, though. With the notable exception of the Web server benchmark, where data rates of the hybrid setup do, in fact, approach what we'd expect from the pure SSD configuration, the mixing SSDs and hard drives isn't able to get anywhere close to an SSD-only arrangement.
The Adaptec controller fares much better in the hard disk I/O performance tests. Regardless of benchmark type (database, file server, Web server, or workstation), the RAID 6805 controller goes head-to-head with Areca's ARC-1880i and LSI's MegaRAID 9265-8i and consistently achieves first or second place. Only the HighPoint RocketRAID 2720SGL trails in the I/O performance benchmark. Replacing the hard disks with SSDs, LSI's MegaRAID 9265-8i shines and leaves the three other controllers in its dust.
