Western Digital (and probably Toshiba and Seagate) have been shipping drives that use shingled magnetic recording (SMR) and leaving the fact off of their product and usage guides. There is lots of talk around here about using perpendicular magnetic recording (PMR) drives in our TiVos. But it seems WD (and maybe Toshiba and Seagate) are shipping SMR drives and hiding the fact from us. More info here: Western Digital admits 2TB-6TB WD Red NAS drives use shingled magnetic recording – Blocks and Files And here: Seagate 'submarines' SMR into 3 Barracuda drives and a Desktop HDD – Blocks and Files And here: Shingled hard drives have non-shingled zones for caching writes – Blocks and Files Western Digital is saying these drives use "Drive Managed SMR" meaning the drive itself manages garbage collection and TRIM. They say the drives should be fine in any use except heavy duty enterprise situations. In normal use the drive will manage itself during idle times.