Managing RAID on Linux

Hardware

Hardware RAID means that arrays are managed by specialized disk controllers that contain RAID firmware (embedded software). Hardware solutions can appear in several forms. RAID controller cards that are directly attached to drives work like any normal PCI disk controller, with the exception that they are able to internally administer arrays. Also available are external storage cabinets that are connected to high-end SCSI controllers or network connections to form a Storage Area Network (SAN). There is one common factor in all these solutions: the operating system accesses only a single block device because the array itself is hidden and managed by the controller.

Large-scale and expensive hardware RAID solutions are typically faster than software solutions and don’t require additional CPU overhead to manage arrays. But Linux’s software RAID can generally outperform low-end hardware controllers. That’s partly because, when working with Linux’s software RAID, the CPU is much faster than a RAID controller’s onboard processor, and also because Linux’s RAID code has had the benefit of optimization through peer review.

The major trade-off you have to make for improved performance is lack of support, although costs will also increase. While hardware RAID cards for Linux have become more ubiquitous and affordable, you may not have some things you traditionally get with Linux. Direct access to developers is one example. Mailing lists for the Linux kernel and for the RAID subsystem ...