Thursday, April 21, 2011

No desktop drives in RAID?

WD Black Caviar
Some of the fastest and well rated large capacity desktop drives are WD Black Caviars. They also 50%-100% less expensive than their "enterprise class" RE4 series siblings. Can you use them in RAIDs? Western Digital says "no" in their spec sheet:
  • "Desktop / Consumer RAID Environments - WD Caviar Black Hard Drives are tested and recommended for use in consumer-type RAID applications (RAID-0 / RAID-1).
  • "Business Critical RAID Environments – WD Caviar Black Hard Drives are not recommended for and are not warranted for use in RAID environments utilizing Enterprise HBAs and/or expanders and in multi-bay chassis, as they are not designed for, nor tested in, these specific types of RAID applications. For all Business Critical RAID applications, please consider WD’s Enterprise Hard Drives that are specifically designed with RAID-specific, time-limited error recovery (TLER), are tested extensively in 24x7 RAID applications, and include features like enhanced RAFF technology and thermal extended burn-in testing."
Also in their KB article:
"Western Digital manufactures desktop edition hard drives and RAID Edition hard drives. Each type of hard drive is designed to work specifically as a stand-alone drive, or in a multi-drive RAID environment."
There is more detailed information in that KB article:

"When an error is found on a desktop edition hard drive, the drive will enter into a deep recovery cycle to attempt to repair the error, recover the data from the problematic area, and then reallocate a dedicated area to replace the problematic area. This process can take up to 2 minutes depending on the severity of the issue. Most RAID controllers allow a very short amount of time for a hard drive to recover from an error. If a hard drive takes too long to complete this process, the drive will be dropped from the RAID array. Most RAID controllers allow from 7 to 15 seconds for error recovery before dropping a hard drive from an array. Western Digital does not recommend installing desktop edition hard drives in an enterprise environment (on a RAID controller).
"Western Digital RAID edition hard drives have a feature called TLER (Time Limited Error Recovery) which stops the hard drive from entering into a deep recovery cycle. The hard drive will only spend 7 seconds to attempt to recover. This means that the hard drive will not be dropped from a RAID array. While TLER is designed for RAID environments, a drive with TLER enabled will work with no performance decrease when used in non-RAID environments."
In other words, WD is OK with Black Caviars for home and gaming use in RAID0 and 1, and is not OK with using them in external enclosures - even in RAID0.

Compare that to Deskstar 7K3000 desktop hard drives whose maker Hitachi says they are suitable for:
  1. "Consumer and commercial computers"
  2. "Video editing arrays"
...with no explicit warnings against commercial or enterprise class RAID configurations.

Bottom line, Hitachi supports their desktop drives in high performance arrays while WD doesn't.

What is your experience with using desktop drives in RAIDs?

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