Use of 2.5" Laptop Drives in a Server?
In addition to the problems above, you may have additional issue running these drives in RAID configuration due to the lack of TLER. (If you are considering a model without.) This quote references desktops and the RAID Edition drives but I imagine the same to be true in the 2.5" line if you substitute in "notebook" and "enterprise" or "SAS" where applicable.
Western Digital manufactures desktop edition hard drives and RAID Edition hard drives. Each type of hard drive is designed to work specifically in either a desktop computer environment or a demanding enterprise environment.
If you install and use a desktop edition hard drive connected to a RAID controller, the drive may not work correctly unless jointly qualified by an enterprise OEM. This is caused by the normal error recovery procedure that a desktop edition hard drive uses.
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. Though TLER is designed for RAID environments, it is fully compatible and will not be detrimental when used in non-RAID environments.
The biggest difference? Failure-rate.
Those 'enterprise' drives are warrantied for 5 years, whereas the cheaper ones are probably warrantied for less. Also look into the spec-sheets for them and look at their duty-cycles. The Enterprise drives are designed to run for 5 years straight, where the 'desktop' drives are designed to run 8 hours a day for 5 years. Very different use-cases and will impact your drive failure rates.
A second thing to look at is a line on those spec-sheets named "Nonrecoverable Read Error rate", which is a measure of the frequency of bits that are unable to be read inside the recovery window.
As of this posting (8/16/2011), the Seagate Savvio 10K.5, a 10K RPM Enterprise 2.5" drive, has its rate listed as 1x10^16. The Western Digital Scorpio Black, a 7.2K RPM consumer oriented 2.5" drive, has its rate listed as 1x10^14 bits. By this measure, the Savvio drive is two orders of magnitude more reliable.
This error rate puts an upper limit on how large of a RAID5 set you can build with such drives. When a drive fails in a RAID5 array, the array then has to read the entire RAID volume in order to rebuild the parity. If a non-recoverable read error occurs, you can lose the entire RAID set. Some RAID cards can get around this, others can't. They're not all built the same.
The above error-rate measures are approximate, but are the point where such errors are more likely to happen than not.
- 10^14 bits = 12.5 TB
- 10^16 bits = 1.25 PB
Only, you don't want to build arrays that large. The largest you want to build them is about 50% that size to minimize the likelihood of the rebuild failing. For those really cheap 1TB 2.5" drives, you can only fit 7 of those in a R5 array, where with the more expensive 10K RPM drives you could fit 15 of those 900GB drives in an array and feel safe in the knowledge that it'd rebuild just fine (but take a long time); your parity-losses are worse with the cheaper drives, which impacts your overall capacity.
Apparently everyone saying to use enterprise drives...just because...are mistaken.
There are several articles from companies that have actually done this vs just making stuff up.
In short: enterprise drive failure rate 4.6%, consumer drive failure rate 4.2%.
I really hate it when a well thought-out, passionate argument is destroyed by one tiny ugly little FACT.
https://www.backblaze.com/blog/enterprise-drive-reliability/