Hardware- vs. Software-RAID. Which one to choose? - TUXEDO Computers

TUXEDO systems equipped with at least two storage devices are generally suitable for setting up a RAID array. RAID stands for Redundant Array of Independent Disks and refers to a method in which multiple physical drives appear to the outside world as a single logical drive. Reasons for using RAID include increasing fault tolerance through redundancy or improving data throughput.

Hardware vs. Software RAID

A basic distinction is made between hardware and software RAID. With hardware RAID, the intelligence resides in a dedicated RAID controller. This usually comes in the form of an additional expansion card and typically features its own processor, cache, and optionally a battery or supercapacitor to protect the write cache. To the operating system, a hardware RAID appears as a single drive; the individual disks are not visible to the file system. Advantages mainly arise in classic server environments with sustained high loads. However, these are offset by disadvantages such as higher costs, strong dependence on the specific controller, and limited recovery options in the event of a defect.

Software RAID

With software RAID, the Linux kernel itself manages the RAID array. Traditionally, this is done via mdadm, often in combination with LVM. When using Btrfs as the file system, *mdadm* is not required, as Btrfs has internal RAID functionality built in. At the operating system level, the individual drives remain visible and are assembled into the RAID at runtime. This variant is flexible, vendor-independent, and on modern hardware causes virtually no measurable performance penalties.

Fake RAID

A special form of software RAID is so-called fake or host RAID, which is found on many mainboards. Here, a hardware RAID is merely simulated. In reality, it is a standard disk controller with additional BIOS support but without dedicated RAID hardware. From a Linux perspective, this solution offers hardly any advantages while increasing complexity and dependence on firmware and drivers.

Software RAID as a Recommendation

If you want to set up a RAID on our systems, we explicitly recommend using software RAID. It supports the RAID levels RAID 0 (striping), 1 (mirroring), 4, 5 (distributed parity), 6 (double parity), and 10 (mirrored striping). In addition, it offers features such as easy expandability, hot spares, and a high degree of independence from specific hardware.

RAID levels 1, 4, 5, and 6 can also be expanded while the system is running by first adding additional drives as hot spares and then integrating them into the existing array. The array remains online, and resynchronization runs automatically in the background.

RAID Level Comparison

¹ Fault tolerance with RAID 0: RAID 0 provides no protection against data loss. Data is distributed across all drives in the array to increase speed. If just a single drive fails, all stored data is irretrievably lost.

² Degraded mode: A RAID array is in a degraded state when a drive is no longer readable and is removed from the array. New data and parity information are then written to the remaining drives. If a data request involves the failed drive, it is reconstructed using the parity data from the other drives.