Hello John The number of HDDs in either of your RAID 6's should be fine. As you increase the number of drives in an array you decrease the reliability of the array. You are more likely to have multiple failures that cause data loss with large arrays. I wouldn't worry too much about it with 12 drives, but expanding beyond that I would start considering the cost versus reliability. The stripe size will be dependent on the data. If you will have primarily large blocks of data written to the drive then you may want to have a large stripe size to increase performance and better utilize available drive space. If there will primarily be small blocks of data then a small stripe size will save a lot of drive space. If you don't know or it will be a mixture then I would leave it at the default. I think the default is 64 or 128k. Another thing to keep in mind is that the OS partition will still be on the same volume. If you are not going to separate the OS from the data by putting it on it's own array then you will need to be sure to install with the system board set to UEFI mode and use GPT when installing the OS. If you don't then only 2TB will be seen by the OS. Thanks
Couple of config questions if I may:  1) We have 2 PowerEdge R720XD servers with the "PERC H710p Integrated RAID Controller, 1GB NV Cache" installed. Each server has 24 x 1TB 7.2K RPM, 6Gbps Near Line SAS 2.5" Hot Plug Hard Drive  I was going to configure 2 LUNs on each of these servers, each LUN consisting of 12 drives RAID 6.        The OS will be installed on a 200GB partition on the 1st LUN on search server. Servers have 32 GB RAM, so I don't expect any swapping. These servers are for backing up the user data on workstations (desktops and laptops). Each workstation backed up has its own archive folder which is a property database consisting of multiple files, a small number of metafiles and large data archive files that grow to 4GB in size before it creates a new one.  2) A related question is: We have 4 PowerEdge R420 servers with the "PERC H710 Integrated RAID Controller, 512MB NV Cache" installed. Each server has 8 x 900GB 10K RPM, SAS6 2.5 " Hot Plug Hard Drive   I was going to configure a single LUN on each of these using all 8 drives RAID 6.      The OS will be installed on a 400GB partition on the LUN on search server. Servers have 32 GB RAM so I don't expect any swapping.   These servers are used for workstation management, mostly deploying software packages and inventorying the workstations. The management application has a handful of database files for storing the inventory data, about 200 MB and this primarily lives in RAM. The software packages it deploys to the workstations range in size from 5MB - 10GB and are basically ready only. The database files will be located on the OS partition and the packages on the 2nd partition. Thx again, :emotion-2: John Bradshaw  
Configuring Raid optimally for R720xd and R420 servers