Fun with a cheap and powerful Serially Attached SCSI card and 15,000 RPM drives in a blistering RAID 0 configuration.Fundamentally, mechanical hard drive technology hasn’t advanced all that much in the many years since its inception. In spite of the ever increasing speeds and capacities, we still have rotating platters being accessed through mechanical heads.
The major breakthroughs have been in interfaces, such as SATA (Serial ATA). These have provided a dedicated link between the drive and the controller with a smaller cable, and in the process relegated ribbon cables to the technological graveyard where they are now fulfilling the role of keeping laserdiscs and old iMacs company.
The same technology has made its way into the enterprise market, where the old SCSI standard has been superseded with SAS (Serially Attached SCSI). It provides a physically similar connection to SATA, however it still uses all the tried and true SCSI commands and adds extra features such as more bandwidth, redundant controllers and better management features.
Fundamentally SAS takes the bulletproof (thousands of network engineers just cried out in pain when they read the word “bulletproof” in the context of hard drives) design of SCSI and delivers it through a similar interface to SATA. The result is smaller cables, which make cooling more effective, and the flexibility of using either SAS or SATA hard drives in an array.
Adaptec has released its $599 3405 card, which provides PCI-e SAS RAID, managed in hardware. This places it in the same price bracket as many other PCI-based hardware SATA RAID cards, however being in its price bracket and simply being a PCI-e based card means it gets a lot of bonus points compared to other traditional PCI-based SATA-only cards you could compare it to.
The PCI-e interface is a big plus as it keeps the easily crowded PCI BUS free. RAID cards will very happily chew through all the bandwidth a 32-bit 33MHz PCI bus can supply, which is why higher end RAID cards are actually built to connect through PCI-X connectors, but will grudgingly fallback to 32 bit 33MHz PCI speeds if that’s all they are plugged into. PCI-e also adds some future-proofing to the card.
If you think about what kinds of machine this card will be plugged into, it’s not just the bandwidth saving that you can look forward to. Pseudo workstations built from high end consumer components are popular with animators and video editors, and PCI can become a rarity on those motherboards once sound cards are installed or they become covered by dual slot graphics cards.
SAS is also a better option than SATA because not only will the SAS system support both SATA and SAS drives, it will talk to expanders too. That means one card can address multiple drives in an active enclosure and manage them all from within the card’s BIOS. This is how many of the monster 19” rack mount drive arrays already on the market are connected to servers.
Setting up an array with the 3405 is a simple matter of jumping into the card’s BIOS and lashing together a few drives. We did exactly this to test, but went through multiple RAID 0 configurations with some spectacularly powerful 15,000 RPM SAS drives as well as our test bench hardware. We wanted to make sure the card would play nice with the most vicious hardware we could get our hands on as well as the more pedestrian SATA hard drives that make up our test bench. Seagate came to the party and delivered some 15,000 RPM SAS drives for testing purposes: two Cheetahs and a Savvio drive.
We fired up HD Tach and tested the card with various hard drive configurations in RAID 0. The results were pretty breathtaking...
|MB/s Average||MB/s Burst|
|3x15K + 1x10K||264.533||467|
|2x15K + 1x10K||234.533||456.033|
The SATA drive in question is a 10,000 RPM Western Digital Raptor. We can infer that although blindingly fast SAS drives do increase performance, supplementing them with SATA drives will nonetheless bring performance improvements if you’re after sheer RAID 0 transfer speed. The power of SAS doesn’t lie here though. Enterprise drives need to be highly reliable, and reliability isn’t something that you can test for, but it is reflected in the warranties and cost of SAS drives. They also need extremely fast random access times so that servers don’t spend as much time waiting for their data to arrive.
Unsurprisingly, the Adaptec card is capable of supporting both interfaces. If you’re after the best sustained transfer speeds you’d be better off using high capacity SATA hard drives, as their high data density will result in more information passing under the drive heads and into your computer.
Like any piece of high end hardware you will need some drivers for the 3405 (we were using Windows but there are Unix, Linux, Sun and Novell flavours available) and a bit of setup time. The Windows management software is also useful.
Underneath the card’s heatsink lies a dedicated processor, which gets spectacularly hot. We recommend using this card in a case with good airflow, or the cunning placement of a fan or two in a case without good airflow. It’s a half-height card, and the package includes a full and half height bracket and breakout cable that terminates in four SAS connectors which will also plug into differently keyed SATA connectors.
RAID levels 0, 1, 1E, 5, 5EE, 6, 10 and JBOD are supported, and with an expander you can also use level 50 or 60. If you really wanted to prove a point and had enough expanders you could hang 128 drives off the one card.
Stack the flexibility of the card next to its price and it’s a very tempting option. We recommend anybody who is planning a hardware RAID give it some serious consideration.