How to Build a RAID-Capable Storage Server

This was among the driving forces behind the development of the Serial ATA standard, which showed potential to address these issues. Now in its second revision, SATA is delivering what system builders have sought for years: good performance at an affordable price.

But the SCSI standard has not remained stagnant, either. Serial technology is everywhere. The newest SCSI standard—called Serial Attached SCSI, or SAS—is perhaps the ultimate convergence of ATA and SCSI technologies.

How does this benefit the server system builder? Let's find out by taking a look at SATA-II and SAS. Then, we'll build a RAID-capable server with SATA-II drives that can later be migrated to SAS drives while still preserving our hardware investment and without the need to rebuild the entire system from the inside out.

Summary of the Technologies

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SATA-II offers some important improvements over the original SATA hardware standard. The SATA-II Working Group sought during development to ensure physical compatibility with upcoming SAS interfaces, and an agreement was worked out with the SCSI Trade Association to make this happen. This is an important reason why system builders now have the option of running SATA-II drives or SAS drives on the same backplane. SATA-II also carries forward the main improvements of SATA which are low cost, simplified cabling and connections, and backward compatibility for drivers and software.

SAS is the other side of the "convergence equation." The SAS standard and the protocols within it is what enables communications between SATA drives and SAS controllers. There are actually three different protocols available to SAS. These protocols are known as Serial SCSI Protocol (SSP), SCSI Management Protocol (SMP), and SATA Tunneled Protocol (STP). As you might imagine, SSP transfers SCSI commands across the data link to a drive, while SMP sends management information to an expander attached to the controller.

The real beauty, however, is STP. This is what enables SATA commands to be sent from an SAS controller to a SATA drive. Since the SAS connections are point-to-point instead of shared, we can have SATA-II drives and SAS drives installed within the same enclosure, and the controller can successfully negotiate the connection.

To the system builder who handles servers, RAID is not an option, it's a requirement. While increasing the number of drives in the system increases performance, it also introduces additional points of failure. This became a bigger problem with ATA RAID systems in the past, due to a longer error recovery process and lower Mean Time to Failure (MTTF) specs than SCSI drives. Also a problem for early ATA RAID systems was the lack of true hot-swap capability. Manufacturers are now addressing these issues with their versions of SATA and SATA-II drives designed specifically for use in RAID systems. This enables the system builder to create SATA RAID systems that are viable in production environments and are better able to compete with SCSI arrays. The convergence of SATA-II and SAS takes this concept to the next level.

Ingredients

For our recipe, we will use components from Adaptec and Maxtor. Here's what you'll need:

Drive Enclosure: I recommend Adaptec's 335SAS, which fits four 3.5-inch SATA or SATA-II or SAS hard drives into the space of three consecutive 5.25-inch half-height chassis bays. This unit is available in either beige or black, with an MSRP of just under $370. Outstanding features of the 335SAS include: support for enclosure management, integrated cooling fan, redundant power connectors, and hot-swap capability. Here's a look at the Adaptec 335SAS drive enclosure:

Controller: Also from Adaptec is the 4800SAS RAID controller, which is an 8-port controller supporting SATA or SATA-II or SAS drives. This model, with an MSRP of $945, supports standard RAID levels 0, 1, 5, 10, and 50, plus Adaptec's advanced RAID levels 1E, 5EE, and 60. The 4800SAS card has a PCI-X bus interface, which has excellent backward compatibility with existing PCI slots. A PCI-X card can be installed in a system with a 64-bit 66 MHz PCI slot or even a 32-bit PCI slot, in addition to the 64-bit 133 MHz or 100 MHz slots. The PCI bus interface is almost ubiquitous now; therefore, a PCI-X card such as this can be used to upgrade an existing platform with an open PCI slot on the motherboard. For new systems where this type of backward compatibility is not a concern, Adaptec's 4805SAS controller has a PCI-Express x8 interface and otherwise identical specifications. Here's a look at the Adaptec 4800SAS RAID controller:

Hard Drives: I recommend the Maxtor MaXLine Pro 500, which is a 500 GB, 7200-rpm SATA-II drive with a 16 MB buffer. This is an enterprise-class drive with improved Error Detection and Recovery features to improve reliability in RAID systems. The MSRP is around $300 each, giving this product an excellent price-to-performance ratio. Here's a look at the Maxtor MaXLine Pro 500:


Seven Steps To SATA

Make sure you observe all usual precautions such as removing power from the system and discharging static electricity build-up before you begin. To be safe, wait one minute after powering down your system and removing the cord from the power supply. Touch a grounded piece of metal before you begin working, to discharge static electricity. This may not seem important, but following these measures can promote the longevity of your system. Waiting after powering off is necessary to give capacitors in the system a chance to discharge completely and for standby power to dissipate. If you do not do this, you may either destroy components during assembly or contribute to an untimely system failure during operation.

If you are upgrading an existing system instead of building a new system, make sure you follow the usual backup and recovery procedures to keep your data safe. This is important, because data is destroyed when drives are initialized for inclusion in a RAID array. Also, you may not have a means of transferring data within the system when you're replacing the entire storage array. If this is the scenario you face, then you'll need an external backup that will handle all of your data at once. If you decide to re-install your software from scratch, be sure to get an image before you start, or at least make copies of your most important files.

Step 1. Install the Array Controller: Open the chassis and find an open PCI slot on the motherboard for the 4800SAS controller. For best performance, use the fastest slot available. If your motherboard has an open PCI-X 133-MHz slot, use it. Gently press the card into the slot until the card slips into place with the motherboard and chassis; then secure the card with a screw or other retention mechanism provided with the chassis. While there are no jumpers or switches to set, leave the chassis open as you move to the next step.

Step 2. Install the Drive Enclosure: The drive enclosure is installed through the front of the chassis from the outside. If your chassis requires mounting rails for the 5.25-inch bays, screw those onto the outside of the drive enclosure before sliding the assembly into the bay. Adaptec's kit comes with brackets, screws, and cables.

Step 3. Install the Hard Drives: The hard drives are held in the enclosure with individually removable carriers. The drives are secured in their carrier by two screws on each side. Unlock a carrier by pressing the lever button in; then pull the lever outward to free it. Next, pull each carrier out the front of the enclosure and screw a hard drive into place. Then push the drive/carrier assembly back into the bay and lock into place. Repeat as necessary to install all of your drives.

Step 4. Connect the cables: Now that you have all of the hard drives installed into the enclosure, it's time to connect the cables to the controller. This is why we left the chassis open in step 1: We still have easy access to the inside of the system. You should use the SAS fan-out cable included with the drive bay. One end of this cable connects to the SAS connector on the controller. The other end fans out into four individual connectors that plug into the back of the enclosure.

Step 5. Upgrade and/or configure the controller's BIOS: Once you snug up all the connections and close the chassis, you can boot the system. This is a good time to glance at the controller's firmware version. By checking Adaptec's support Web site, we can find the current revision level and make sure we meet it. If not, upgrading the RAID controller's BIOS is a process remarkably similar to upgrading a motherboard BIOS. If you need to upgrade, enter the controller's menu by pressing CTRL-A at boot, follow the prompts, and reboot the system. If your firmware is current, proceed to the next step.

Step 6. Create an array: You have the choice of creating an array from either the controller's BIOS utility or software on a bootable CD-ROM that is included with the controller. I prefer using the BIOS, and Adaptec also recommends this method. However, you should familiarize yourself with RAID arrays before performing this step. (There is downloadable information on Adaptec's Web site if you need help.) Also, while it is possible to have a mix of SATA and SAS drives attached to the same controller, I do not recommend that you create an array containing both SATA and SAS drives.

Select your controller in the menu if you have more than one in the system. Then select Initialize Drives from the menu. Next, select the drives you want to initialize. Once the initialization is complete, select Create Array and choose the array properties. With these parameters finalized, the array builds and you are ready to move on. It is possible to use the array while it is building, but you will experience performance degradation until it is finished. Instead, I recommend that you let the build process complete itself before you attempt to load the software, even though this is time-consuming.

Step 7. Install the software: You will need to create a floppy disk with the device driver for the controller by booting the system from the RAID Installation CD included with the controller kit. Follow the menu prompts on the screen to get to the Adaptec Start Menu. Then select Create Driver Disk. Again, follow the prompts according to your OS. Reboot the system when you're done, booting from your operating system CD. Then begin the installation, inserting the driver disk you created when the system prompts for it.

As a system builder, you can use this recipe to improve your server products for higher sales and more satisfied customers. You will also see fewer service calls due to the high reliability of these storage components.

DAVID GILBERT is the owner of Appalachian Computer Systems, a system builder based in West Virginia that specializes in multiprocessor SCSI RAID servers.