Can Heterogeneous RAID Arrays Work?

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Homogenous Vs. Heterogeneous RAID

RAID arrays look simple, but depending on the configuration, they can become rather complex and require IT administrators to pay a lot of attention to hardware and settings. There is one topic, however, that all storage professionals typically agree on: RAID array hard drives should be identical, meaning that the same drive with the same firmware should be used. Using the same hard drives is usually crucial for large enterprises, where vendors devote much time and energy to test and implement different hardware to see if systems work like they should. However, small- and medium-sized businesses might feel compelled to take a more home-grown array approach. It seems logical to mix existing hard drives with new ones, which is what we did for this article.

Although prices for hard drives have decreased considerably over the last couple of years, storage represents a major part of every company’s IT budget. And the importance of storage is increasing, as more and more data needs to be handled, while more and more products and media are being used. As you move from organizing personal data to managing corporate information, issues such as redundancy, performance, reliability, scalability, manageability, component complexity and pricing add up to a rather complex equation. (Compare Prices on RAID Arrays)

Storage arrays based on RAID technology are a key element in every mission-critical system that requires high reliability and uninterruptible uptime. RAID can be operated with few or multiple hard drives and simple or redundant RAID levels.

Many RAID alternatives exist. You can select between hardware-assisted RAID with powerful I/O processors or host-based RAID, which taxes the system processor for RAID parity calculation. Then you need to choose an interface: this can be either SAS (Serial Attached SCSI) or SATA (Serial ATA). Professional SAS controllers can operate both SAS and SATA drives, while SATA controllers can only run SATA hard drives. Once this choice has been made, you’ll have to decide whether you want to attach drives externally with eSATA or SAS expanders and multi-lane cables. Other options consist of the deployment of hot spare drives, using cache memory on the controller and finally backing up cached content using a battery backup unit (BBU) for the RAID controller. Possibilities are endless and administrators thus usually deploy identical hard drives for RAID setups to reduce complexity.

This typically also includes firmware versions, which should be identical for the sake of performance. We have to agree when it comes to highly customized and optimized RAID arrays, where maximum of I/O performance is crucial for a very specific workload. However, we wanted to know what the difference really is, so we created one RAID set using four identical 320 GB Samsung SATA hard drives and another set consisting of two Samsung drives, one Seagate device and one Western Digital hard disk drive.

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Patrick Schmid was the editor-in-chief for Tom's Hardware from 2005 to 2006. He wrote numerous articles on a wide range of hardware topics, including storage, CPUs, and system builds.

1 Comment Comment from the forums

Typically, I'd say, run RAID-1. When it's time to upgrade, get two more identical drives, plug-em in and set up another mirror. Then, for Windows, delete your system hdd from the device manager and reboot to a Norton Ghost CD (assuming it supports your raid controller). Clone the partitions to new mirror. Power off, remove old mirror, boot to a new mirror. It will most likely re-detect the new mirror and request a re-boot, after that you're good to go on. Old drives can be wiped and sold on e-bay. Or turned into a backup volume.
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