The difference between desktop-series HDD drives and server-series

One very important difference is the Time-Limited Error Recovery (aka Command Completion Time Limit)

Time-Limited Error Recovery (TLER) is a name used by Western Digital for a hard drive feature that allows improved error handling in a RAID environment. In some cases, there is a conflict as to whether error handling should be undertaken by the hard drive or by the RAID controller, which leads to drives being marked as unusable and significant performance degradation, when this could otherwise have been avoided. Similar technologies are called Error Recovery Control (ERC), used by competitor Seagate, and Command Completion Time Limit (CCTL), used by Samsung and Hitachi.

This is very important in RAID arrays where one drive can lock up or degrade the array.

According to Intel's Enterprise-class versus Desktop-class Hard Drives, enterprise-class drives are often faster and more reliable due to better hardware and different firmware.

Better hardware specs:

• better mechanics for faster and more reliable data access (stronger actuator magnets, more servos)
• more cache memory
• more components for error detection and correction
• vibration compensation or reduction to reduce likelihood of data corruption induced by moving parts in the server, e.g. rotating fans and spinning disks

Behavior:

• Time-limited error recovery (TLER) for more reliable and lower-latency error recovery and fail-over
• End-to-end error detection
• Usually fixed rotation speed
• Energy-saving mechanisms that shorten overall life of consumer-grade disks, such as Western Digital's WD Green series' IntelliPark which parks the hard disk after 8 seconds (!) idle time (however, there are tools from the manufacturers and third parties that modify the default settings so that you could use such disks in server or NAS/SAN systems, e.g. idle3-tools).

Testing:

• It's just a guess, but it may be that manufacturers test their enterprise-class disks more thoroughly than their desktop disks, however, independent testing by external parties is not entirely conclusive and might even show that desktop drives may be as reliable as server-grade drives, at least in the initial years of operation (Backblaze study).
• The point here is though that there are more and older desktop drives out in the wild and in active use than enterprise disks, so one could say that we have more and better data about desktop drive reliability than we have for server disks (Google).

Warranty:

• Enterprise-class disks often come with longer warranty than desktop disks. However, this will probably not matter very much to you if you have sensitive data stored unencrypted on your failing disk and do not want to send in your disk to claim the warranty.

Nonetheless, the issue about TLER might be the main reason for choosing server-grade storage solutions over consumer products, especially when operating RAID systems and servers with time-critical workloads like web or database servers.

Other than that, yes, there is probably some FUD by the manufacturers to make you feel uneasy about using desktop products for a server, so using enterprise products will also give you some peace of mind.

THE most important difference is the level of Vendor Support.

If you don't use "hardware compatible" equipment (i.e. OEM) then you may find yourself SOL when the kit dies and you need to get it fixed quick.

Enterprise hard disks also tend to have a longer MTBF (Mean Time Between Failures), i.e. longer life span, than consumer grade ones.

The heat-pad under a smooth chip (motor controller) is missing in the most of the consumer drives (seagate, WD), but is usually present in the most of the enterprise class disks. (so the tiny smooth chip is much more likely to die under the load from overheat in the desktop model). Also enterprise drives usually have a couple of the vibration sensors. Rubber anti vibration dumpers and rigid cases are strongly recommended for all modern high density disks/fan mounts. (Esp ones over with density 500GB+ per platter, since their heads are really fragile from my experience).

Two things:

• Cache size
• Marketing

Reliability is not a distinguishing factor.