Tier Storage with SAS drives

Is it possible to have hot storage on HDD?

I have a HP disk storage shelf with 25 900GB 6G SAS 10K rpm in a raid 10 configuration. This provides about 10TB of file storage data for users home directory and shared directories which is almost full. A lot of the files are old rarely access files, but are still required for reference. I don't want to purchase any more high quality storage and would like purchase  slower higher capacity drives like a HP D2600 w/12 4TB 6G SAS 7.2K.

So my question is can these different disk shelves be used in a tier storage arrangement.

Thanks in advance.

Adrian