Don’t just go by MTBF hours and marketing-speak. Not all of those “NAS optimisations” are good for desktop use.
Before we get into that, we have to take a quick look at assumptions inherent in the design of desktop HDDs vs enterprise/NAS/RAID HDDs. In a desktop, engineers assume that drives are on their own and contain the only copy of user’s data. That means if data is requested from a sector and the disk is unable to read it the first time, it should keep trying until it is successful, or failing that, to take alternative measures, e.g. returning read error, marking sector as bad, remapping sectors, etc. This process takes quite a while, resulting (usually) in system non-responsiveness for many seconds, but at least you get your data instead of the disk just giving up after a few tries.
In a RAID system, this is not necessarily a good thing. Drives are typically part of a storage array, often RAIDed, so it does not carry the only copy of data. If a read error is encountered, it is safe to return a read error after a few failed tries. The RAID controller then marks the sector bad, rebuilds the lost data from other data+parity blocks (this is what RAID is for), and life goes on.
However, if the drive’s built-in error recovery system kicks in, it ends up trying to retrieve the data continuously. The disk doesn't respond for a long time, and the RAID controller takes this as a sign that the disk is down, and kicks it out of the array. The RAID array thus gets degraded just because of a read error in one sector alone—quite pointless. Red drives thus have an additional feature, labelled by WD marketing as TLER (goes by other names on other brand hard drive lines; see below). This provides a user-configurable setting to determine how long the drive should attempt error recovery before giving up, so it does not get kicked out of the array.
The Reds come with TLER enabled by default (their target market is for NAS after all), with a value of 7 (seconds). If you’re using it as a standalone drive, you probably do not want this, unless you like having more read errors than normal (i.e. without TLER). Unfortunately, WD’s TLER utility for Windows doesn’t work on the Reds (or so the internets tell me), so you’ll either have to learn some
smartctl trickery (better RTFM!), or buy something that’s
more in line with what you want (3TB models are going for $180 at time of writing; slightly more than the Reds and Seagates, but all things considered I think you’re better off paying the difference).
More info on TLER at
http://en.wikipedia.org/wiki/Error_recovery_control, and on Red drives at
http://www.anandtech.com/show/6157/western-digital-red-review-are-nasoptimized-hdds-worth-the-premium/2.
