My ramblings on the stuff that holds it all together
Category Archives: RAID
What I found interesting was a link to a page on the Western Digital support site stating that desktop versions of their hard drives should not be used in a RAID configuration as it could result in the drive being marked as failed.
Now, this I far from the best written or comprehensive technote I have ever read however I wasn’t aware of this limitation, it appears that desktop (read: cheap) versions of their drives have a different data recovery mechanism to enterprise (read: more expensive) drives that could result in an entire drive being marked as bad in a hardware RAID array – the technote is here and pasted below;
What is the difference between Desktop edition and RAID (Enterprise) edition hard drives?
Answer ID 1397 | Published 11/10/2005 08:03 AM | Updated 01/28/2011 10:00 AM
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.
If you install and use a desktop edition hard drive connected to a RAID controller, the drive may not work correctly. This is caused by the normal error recovery procedure that a desktop edition hard drive uses.
Note: There are a few cases where the manufacturer of the RAID controller have designed their drives to work with specific model Desktop drives. If this is the case you would need to contact the manufacturer of that controller for any support on that drive while it is used in a RAID environment.
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.
There are even reports of people saying WD had refused warranty claims because they discovered their drives had been used in such a way, which isn’t nice.
This is an important consideration if you are looking to build or are using a NAS for your home lab like a Synology or QNap with WD HDDs or maybe this even extends to a software NAS solution like freeNAS, OpenFiler or Nexentastor
It’s also unclear if this is just a Western-Digital specific issue or exists with other drive manufacturers.
Maybe someone with deeper knowledge can offer some insight in the comments, but I thought I would bring it to the attention of the community – these are the sort of issues are like the ones I was talking about in this post but, as with everything in life – you get what you pay for!