Hello. Unfortunately, the PERC 5i does not support 2TB+ drives so that will not work. We also recommend the use Dell certified drives to ensure proper firmware communication also.   The 1x2 flexbay can be found on the web by many third party retailers. Check to ensure that you are getting all 3 cables that should come with the flexbay.  Please let us know if that helps. 
Am in the process of upgrading and putting back together a DPE2900 that was dropped on my lap. Ive replaced both power supplies-   DPE2900 2nd gen,  W2008 R2 server OS,  PERC5i,  YM-158MBo,  16GB RAM, I am looking for input as to the feasibility of the following; 8  - WD Red WD60EFRX 6TB IntelliPower 64MB Cache SATA 6.0Gb/s 3.5" NAS Hard Drive Bare Drives in RAIN 10 for storage, 2  - WD Re WD5003ABYZ 500GB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5" Datacenter Capacity Internal Hard Drive Bare Drives in RAID 1 for the OS.  I also need to find the 1x2 Flex Bay and cabling for this upgrade. Any suggestions and input would be greatly appreciated. 
Poweredge 2900 Hard drive upgrade