Selecting the Best Hard Disk Drive

When consumers look to upgrade their computer hard drives, they tend to look for the most capacity for the lowest cost. In most cases this is not a bad strategy for desktop or home computers. The drives from the top name manufacturers are all fairly reliable. You can find great deals by using sites like http://www.pricewatch.com/ or even searching Google, MSN, or Yahoo. However, if you are purchasing a hard drive for something other than a general purpose desktop computer, then there are other factors to consider.

First of all, if the drive is being purchased for a drive array or a server, then the desktop hard drives are not well suited for this purpose. This includes RAID systems, Storage Area Networks (SAN), and Network Attached Storage (NAS). If you are selecting drives for one of these purposes, then you will be better served by selecting an enterprise class drive or a near-line storage drive.

Differences in desktop hard drives versus enterprise or near-line drives:

  • Desktop drives are not designed for a continuous duty cycle. Enterprise and near-line drives are built to run 24x7.

  • Desktop drives have a much lower meantime between failure rating (MTFB). While desktop drives usually have an MTFB around 500,000 hours, enterprise and near line drives are usually 1,000,000 or more hours. But don't get wrapped up in these MTFB numbers; just like a lot of other published specs, they serve more a of marketing purpose than a reality. Each drive manufacturer tests their own drives using methods and numbers that are going to reflect best on their products. 500,000 hours is over 57 years! No hard drive is going last nearly that long. Not even close! If you get five years out of a hard drive, then consider yourself lucky. The MTFB numbers are actually calculated based on the service lifetimes of a large number of same drive. They can be used for comparison, but the service life or warranty of a drive model is an important factor to be used in conjunction with the MTFB.

  • Enterprise and near-line drives have longer warranties. Now these numbers are worth comparing. If the manufacturer guarantees a desktop drive for one year and their enterprise class drives for five years, then you can safely conclude that the manufacturer expects those drives to last much longer. The numbers are even more significant than you might think. Since desktop drives are typically designed for usage patterns of around 8 hours per day, and enterprise drives are designed for usage around the clock, the manufactures are much more confident in the quality of the enterprise and near-line drives. By the way, the warranty and RMA procedures for all the name-brand providers that I have experience with (Seagate, Maxtor, Western Digital, Samsung, Hitatchi... ) are pretty good. I say pretty good because most of them require you to pay shipping, handling and expediting costs to replace drives that fail due their faulty materials and workmanship.


  • Error correction works very differently in desktop drives as opposed to enterprise and near-line drives. A desktop drive will retry disk operations many times before giving up and reporting an error. A disk operation that should take a split second may take a minute or more in a desktop drive if an error is encountered. The operation may eventually succeed and the desktop computer user will just experience a pause or temporary lockup. Disk array systems are usually designed and configured to recover from errors in a completely different way. They store redundant data on separate disks so if the data can't be accessed on one physical disk, it is always available on another. If a desktop drive is used in an array, the drive itself will attempt to retry for lengthy period of time causing the array logic to timeout and possibly cause the drive to drop from the array. The near-line and enterprise drives usually perform more robust error detection and correction in their caching systems as opposed to retrying the physical disk operation for lengthy period of time.

  • Desktop drives are also optimized for single user access where near-line and enterprise drives are engineered to handle access from many users at the same time. The near-line and enterprise drives have certain firmware commands and capabilities to organize near simultaneous requests so that they can be handled in the most efficient way.

  • Near-line and enterprise drives are usually designed to withstand much more vibration and sustained vibration than desktop drives. Drives that are configured in arrays and server racks are subjected to constant vibration from other drives and equipment. Vibration can accelerate the deterioration of a hardrive and end it's life prematurely.

  • Many of the near-line and enterprise drives are engineered to manage workload by slowing down or validating each read and write when the drive temperature rises. This effectively causes the drives to cool down and continue to operate indefinitely while a desktop drive would fail under similar circumstances.

  • Some desktop drives are designed to spin down during periods of non-use. This saves wear and tear on the drive as well as saves energy. While this may extend the life of a hard drive and be desirable for a desktop computer, it can cause problems in arrays. Array's don't expect to have to wait for a drive to spin up before accessing data. Enterprise and near-line drives have other ways of saving energy, such as powering down parts of the circuitry that is not being used; but not spinning down the drive, which takes much longer to start back up than an micro electronic circuit.

For desktop applications, the drives designed for desktops may be the best choice. They are certainly less expensive and in many cases they are faster for desktop type applications. If you are sensitive to noise, then you can find quieter desktop drives than server or enterprise drives.

There are other types of hard drives that are designed for automotive use, portable devices, appliances and more. Those drives are built for the specific application and environment they are intended to be used in. Heat, vibration, reliability, noise, performance, costs, and access profiles are all factors in designing a hard drive for a particular application. Don't just find the cheapest drive with the most capacity, you may be making a mistake that could put data at an unnecessary risk. Or even worse; a device or system may be more likely to fail that could have even more costly consequences.

3 comments:

powergeek said...

Very informative, thank you. Can you give me any advice about which brands are most reliable?

jazar said...

I don't feel like I have enough data to give advice on the reliability of the different brands of hard drives. I will share with you my experience over the last 2 years and you can use this information however you want to. Keep in mind that my experience may or may not accurately reflect the quailty and reliability of a brand or any particular model.

I have purchased quite a few Seagate and Maxtor drives over the past couple of years. All of them are enterprise or nearline drives. A shockingly large percentage of the Maxtor Maxline III 500GB drives have failed and been replaced by Maxtor. I have had a very small percentage of Maxline III 320 GB drives fail. All of the replacement drives have been the exact same model as the original and none of the replacements have failed so far. After the rash of Maxtor failures, I switched to the Seagate drives and have had very few of them fail. The Seagate drives are used in the exact same model of SAN as the Maxtors and used for the same application.

I suspect that the failed Maxtor drives were from a bad batch and may not represent the Maxtor brand. I have have purchased few of the other brands and don't have any experience with them. For now I am sticking with Seagate.

Maybe some other readers can share their experiences.

Anonymous said...

My maxtor died after about 8 months. I also had a Samsung crash about a year ago. I bought a westen digital and have had no problems.