Volume distribution depends on the IO levels, latency, available space on the member, etc.  The balancer works to make sure the members IO or latency levels are approximately the same when the arrays are active or in a steady state of IO. When a volume requires small, random write performance that R10 offers, over time the volume slices will migrate to the R10 Member.  You can also set the volume RAID preference, as well.  Also a R10 member with 15K disks have less capacity than the R50, 10K.   So more data will be stored on the R50, since data is striped across members in proportion to their relative sizes.   If you haven’t already, take a look at this document: www.dellstorage.com/.../DownloadAsset.aspx -joe
How is volume load balancing calculated?  For instance, say I have 3 PS6110's in a group, all in one big pool. A 15k SAS shelf, 10k SAS shelf, and a 7.2k SAS shelf.  15k is raid 10, and the 10k and the 7.2k are both raid 50.  How will the load balancing of volumes with calculated to move over these arrays? I assume it takes spindle speed into account along with raid type? If not, I guess I'll need to convert the 7.2k to raid 6.  Running firmware 6.0.6
How is volume/block load balancing calculated? 