Linux Software RAID - High Performance through Low-Cost Alternatives

Derek Vadala

Users and system administrators alike frequently find themselves in need of increased storage capacity as well as drive I/O performance. Unfortunately, high-performance drive arrays require an enormous investment overhead and are costly to maintain. Replacing drives in these arrays often costs as much as purchasing several high-end drives from resellers. In the same respect, administrators realize that single-drive solutions do not provide adequate performance upgrades, nor do they provide the high-storage capacities that are necessary to effectively handle large data sets. When most of us encounter these situations, we are usually left with only one option: purchase a high-performance server with RAID capability, while somehow managing to justify the necessity of the expense to management. There is, however, another alternative.

Since release 2.0, the Linux kernel has supported a stock implementation of two RAID levels. Linear concatenation provides a method to quickly combine multiple drives into one drive. This provides increased storage capacity. RAID0, also known as striping, is also a stock part of the Linux kernel and allows users to interleave multiple drives while spreading them across one or more controllers. This provides added storage capacity as well as a tremendous I/O increase. While neither of these RAID implementations support data redundancy, an effort to provide this feature to Linux users began with the release of kernel version 2.0.30. This effort has successfully implemented RAID1 (mirroring), as well as RAID4/5. In addition to providing kernel patches, a set of tools for managing metadevices has been developed, making the implementation of RAID on any Linux system both cost-effective and simple.

The machine used as an example in this article has three Adaptec 2940 Ultra Wide SCSI Controllers. Connected to each controller are two 4.5