Depends on the case temp, where in the case it is, if it's on another drive... normally they are very hot to the touch so maybe 40-50'c but some people say theirs runs cool, so they are all different (brands and models at least) so it's pretty much an unanswerable question.
I've got two drives and one is about 3C to 5C higher in temp than the other one and always gains temp faster than the other one. 40C to 50C is about what they run when gaming or doing other "intesive" tasks.
It could be brand and type of drive also, as the Maxtor SATA drive does not gain much in temp when defragging, while the WD Parallel ATA drive will hit 60C easy when doing this task. This drive is also the one that has a more direct airflow on it. Haven't had any problems yet with it.
Comments
I've got two drives and one is about 3C to 5C higher in temp than the other one and always gains temp faster than the other one. 40C to 50C is about what they run when gaming or doing other "intesive" tasks.
It could be brand and type of drive also, as the Maxtor SATA drive does not gain much in temp when defragging, while the WD Parallel ATA drive will hit 60C easy when doing this task. This drive is also the one that has a more direct airflow on it. Haven't had any problems yet with it.