RAID is one of those legendary geek topics that can work people into a frenzy. Ask any IT manager what their preferred RAID level is and they will have a strong opinion, likely formed over years of experience. Solid State Drives (SSD) have muscled in on turf traditionally held by mechanical drives. But mechanical can still dominate when the discussion moves to max capacity. Today’s SSDs max out around 1 TB while mechanical drives offer up to 4 TB of storage.
I’m not going to get into the ring with anyone to debate RAID levels, but it is worth starting any discussion about RAID with a simple definition:
RAID: Redundant Array of Independent Disks
RAID combines multiple disks into a logical unit for the purpose of data redundancy, performance improvement or a combination of the two. I should note here that I’m referring to hardware RAID rather than software RAID which is implemented at the operating system level.
What I want to discuss today isn’t RAID itself but mechanical drives used in RAID arrays. Most consumers that purchase a computer today consider the drive’s capacity and maybe the brand, but not much else. And that’s just fine. Companies such as Western Digital and Seagate build dozens of drive models that fit every storage need and budget.
RAID Drive Features
Western Digital, Seagate, and others also make a line of drives with features that work best when implemented as part of a RAID array. Let’s take a deeper look at some of the features that set RAID edition drives, like the Western Digital RE (RAID Edition) apart from consumer grade drives such as the popular Western Digital Black drives.
TLER Support – Stands for Time Limited Error Recover. It places a limit on the amount of time a disk can attempt to recover from an error. Consumer drives will attempt to recover and repair errors which can take up to a few minutes. But RAID controllers only allow for a short recovery time (between 7 and 14 seconds) before the controller drops the drives from the array and marks it as degraded. TLER limits the amount of time the hard drive can spend recovering the error which works well for RAID arrays because many types of RAID already have built-in error recovery.
RAFF Support (Rotary Acceleration Feed Forward) – While both RE and Black drives include vibration reduction in the form of StableTrac, the RE drives include a more advanced form of vibration cancelation where sophisticated electronics monitor the drive to correct for both linear and rotational vibration due to sources such as chassis fans and additional hard drives. RAFF improves the performance and reliability of the drive.
SED (Self-Encrypting Drive) – With a motherboard that supports this technology, SED allows the drive to be encrypted using the AES 256 bit encryption engine. SED also includes a feature that allows for the drive to be wiped almost instantly, a time-saving feature for IT manager.
When I worked with customers who were in the process of configuring workstations and servers with RAID, they often asked me if RAID drives outperformed consumer drives like the Western Digital Black or Blue drives. If you were to compare the performance between a single RE drive and one Black drive you’d find them nearly identical in terms of transfer rates because both drives contain the same amount of disk cache and both run at the same 7200 RPM.
What RAID provides is a level of insurance that, if a drive goes down, you’ll be able to continue working with limited interruption or minimized downtime. If your employees use an application that relies on a server running Microsoft SQL Server, performance is important, but keeping that server running, even if a disk crashes, is crucial. This is the type of environment where RAID arrays provide substantial benefits.
Are there any downsides to using drives specifically built for RAID? Well, they consume a bit more power than consumer drives which means they run a little hotter. Neither the RE or Black drivers are the quietest drives on the market, but given most RE drives will be placed in a data center, drive noise is seldom an issue. The RE drives also weigh a bit more, up to a quarter pound.
Price is the last consideration. RAID drives cost 15% more than consumer drives. But you’ll also need to account for the cost of a RAID controller. Many modern server-grade motherboards include RAID supported ports, but they typically only support RAID 0 or 1. For the more advanced levels of RAID you’ll need a dedicated RAID controller card. Intel and LSI are two of the most prominent makers of RAID controller cards. The 4-port cards start around $400 and the quality 8-ports around $750 and up depending on features.
For that price premium you gain a number of features that make for a drive suited for RAID and the demanding tasks found in the enterprise. Keep in mind that having a RAID doesn’t guarantee 100% uptime. The RAID controller could fail as could the software causing downtown. But RAID does help mitigate those risks along with providing a level of redundancy.
Top photo credit: Western Digital