The 1950 has a SAS backplane, which, by specification, will take SAS and SATA drives. Just make sure that you get Dell-certified, Enterprise-class drives ... if this server will carry critical data or services. You can find 2.5" SAS or SATA drives. Dell may be low on stock right now ... I've had good luck with [URL]
I am looking at picking up a Dell 1950 server that has been for sale on Craigslist for a bit.  No HDDs, removed per company policy seller said.  Supposedly it is setup for 4x2.5" drives.  Some of the documentation I've seen from Dell they state that this unit used SAS drives if in that configuration.  Some of the vendor information I've found when I was looking for drive trays and such states that this unit can accept regular SATA drives.  What is the truth here?
Dell 1950 question about HDDs