When we're talking about SSD, the desktop drives use MLC NAND storage, where individual storage bits are grouped - a single delete operation takes out the entire group. TRIM is needed to free up previously allocated space - (basically aggregate groups with "deleted" member bytes - ... brutally oversimplified...).
Enterprise SSD's use SLC NAND - each storage byte is individually addressable. No TRIM is required. Enterprise SSD has a much larger amount of overprovisioning and typically has a much higher PE rating:
About TRIM: it works at the NAN page level, not at the cell level. It is as needed on today's SLC enterprise drives as it is on MLC non enterprise ones. SLC is single level per cell, MLC originally meant multi level per cell but is now taken as a synonim for 2 levels per cells. The latest Samsung range (the 840) now uses TLC, 3 levels per cell. The drawback is less charge per level and therefore less reliability on a per cell level and also less speed.
TRIM/UNMAP on enterprise driveshttp://www.oczenterprise.com/ssd-products/deneva-2-r-sata-6g-2.5-slc.htmlhttp://www.stec-inc.com/support/searchresults.php?cx=018217438920633655538%3A78ha_25djlm&cof=FORID%3A9&q=TRIM
The reason that it seemed there was no apparent TRIM/UNMAP notion on SLC enterprise drives are many. TRIM essentially gives the OS access to some aspects of the drive garbage collection mechanisms. It wasn't needed on drives that had small pages and were always doing intensive garbage collection in the background (basically because they were fast enough to saturate their interface to the world with power to spare for the hidden tasks). Also I/O accelerators as the high end enterprise SSDs are often called are essentially black boxes with no direct exposure to the OS, so there is no need to support an explicitly addressable external TRIM command because there's no OS to use it.
As far as hard drives are concerned
enterprise class hard drives (say RE vs Caviar) are supposed to offer better MTBF, number or load/unload cycles, better vibrational tolerance, etc... All of this is hard for consumers to verify and as it has been pointed out large scale results have been mixed (worth noting: the Google study is now a bit dated and was
also in direct contradiction with IBM studies on the temperature-reliability issue). As an end-user, it is hard to take an informed decision based on the above. Vibration damping should have an impact on performance in absolute terms because it should diminish the number of seek errors, but this is not a feature you can turn on and off in a single drive to check.
Two of the characteristics of the enterprise drives were of interest to customers: the "idle timing" and the error-correction behaviour.
idle timing controls when and how frequently the heads will be "parked" - that an unload/load cycle. Consumer grade drives park frequently after a small duration of inactivity (which is a good thing from a safety and power management pov). But that's a bad thing in NAS and other environments because drives constantly park/unpark.
the error-correction behaviour (Time Limited Error Recovery) leads a consumer drive to very quickly accept a sector as bad when it has difficulties reading it. This may incorrectly invalidate a physical drive in a RAID environment - the controller is willing to wait but the disk already has stopped trying - and that can cause inconveniences or even major catastrophies.
The WD RED series addresses those two issues, at a lower cost than the RE series, and supposedly has better balanced platters (less vibrations), a slightly improved MTBF and a better warranty. Well worth the price differential vs standard drives.
One last thing, but that is the cynic in me talking... the parameters of older WD drives (and other brands) could be adjusted through specific utilities (wdidle was one) and, in some periods, came with better warranties than current WD Red drives. WD Red drives warranties are looking like good value in comparison to standard warranties, but those have been significantly reduced in the recent years. Except for the unverifiable "better balanced platters" issue, the RED thing could be mostly a marketing/product positionning issue.