Dell PowerEdge 1950 how use “raw” disk instead hardware raid Perc 5/i

Hopefully you should be able to reuse your drive trays but remove them and check they have two sets of 4 holes, one for SATA and one for SAS.

If you have the trays that only have holes for SAS you will either need to purchase the interposer cards or different trays. (E.g. to use tray CC852 with SATA you will need interposer PN939, or if you have tray F9541 (I believe also NF467/H9122/G9146/D981C) then no interposers needed).

The SAS backplane and SAS controller will work fine with regular SATA drives. No need for interposer cards for signalling - these help if you have SAS and SATA on the same backplane as the higher voltage SAS signals may not get along with lower voltage SATA).

You've picked 2Tb drives which is the limit of the PERC 5/6. The only issue remaining is whether to purchase Dell drives or not. Dell drives cost a lot more than non Dell drives. The only real difference is that a Dell drive has Dell optimised firmware, and (check with your account manager) Dell should support RAID issues with Dell supplied drives while they may point the finger at your 3rd party drives or even refuse to help.

I've managed to flash a batch of non Dell SAS drives to Dell firmware recently but this may vary from model to model (and possibly even dependant on the firmware the drive comes with). I've only done this for my peace of mind regarding stability rather than to try and trick Dell regarding support though.

Another thing to consider is what type of drives you have connected to the controller. If you've connected consumer grade drives you should be aware that the PERC is expecting a FAST response (as in NOW not 2 or 3 seconds) on a write.