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You can also redirect the output of mdadm to append the ARRAY lines automatically to /etc/mdadm.conf:

# mdadm --detail --scan >> /etc/mdadm.conf

# mdadm --detail --brief /dev/md0 >> /etc/mdadm.conf

But don't forget to edit the file and add DEVICE lines that include all your member disks. You should also add PROGRAM and MAILADDR lines as needed.

Chapter 5. Hardware RAID

Today, nearly every RAID controller manufacturer supports Linux in at least one of its product lines. Furthermore, most of these vendors now provide open source drivers for their cards, although in a few cases, the drivers have been developed by philanthropic programmers. Some vendors have even ported their management applications to Linux, although none of them yet provide source code for these applications. The vendors and products discussed in this section are:

Mylex AcceleRAID 352 (SCSI)

Adaptec 2100S (SCSI)

Promise FastTrak100 (ATA)

3ware Escalade 7500 (ATA)

LSI Logic MegaRAID Elite 1650 (SCSI) and MegaRAID i4 (ATA)

The sections devoted to individual controllers apply generally to other models from the same vendor, since they often share the same firmware and management interfaces. I'll point out any differences of which I'm aware. The introductory sections of this chapter will provide useful information, even if you choose a vendor that I have not covered.

Choosing a RAID Controller

There are quite a number of issues involved in determining which RAID controller to purchase. Chapter 2 covered basic hardware considerations and should help you differentiate between some of the available controllers. Chapter 2 can also help you choose between purchasing a SCSI or ATA controller, which is the first step in selecting a RAID controller.

I would like to point out that although hardware RAID controllers have traditionally been SCSI-only, the demand for inexpensive and consumer-grade solutions has prompted many vendors to include ATA controllers in their product lines. There are even a few companies that specialize solely in ATA RAID controllers. While many vendors now produce ATA controllers, many of them are low-quality and geared toward consumer desktop systems, not servers. One reason for this trend is the increasing omnipresence of ATA RAID on desktop motherboards. This makes it convenient for ATA RAID chipset manufacturers to build RAID cards to supplement their product lines.

However, not all ATA RAID controllers are created equal. There are also some vendors that specialize in high-end controllers that many organizations are now using to create terabyte storage systems at costs much lower than SCSI solutions, and with comparable performance. If you do choose ATA, I urge you to investigate thoroughly the solution you are considering, so that you don't end up with commodity hardware in a server. Some users even purchase ATA RAID controllers only for the extra channels, running Linux software RAID instead of using the controller's RAID capabilities.

Regardless of which disk protocol you choose, RAID controllers share some additional properties that you should consider before your purchase.

Motherboard and System Compatibility

The most important issue to consider when purchasing a RAID controller is its interoperability with the rest of your system. Many controllers are designed specifically to work in server motherboards or with specific motherboard chipsets. Some controllers are even incompatible with certain hard disks and drive firmware. I cannot stress enough the importance of doing your own research before purchasing. When possible, avoid getting technical information of any kind from sales representatives. Instead, check the support section of the vendor's web site for known issues, mine the archives of related discussion lists, and in general, search the Web for user reports about the controller. The Storage Review web site (http://www.storagereview.com) is a good place to look for third-party evaluations.

During my