One reason is that just like any other SAN client for each device the data mover uses there is a limited number of entries in the I/O queue – once that is full it has to wait for an I/O to complete before issueing new ones. If you stripes on multiple dvol’s you increase the number of outstanding I/O – you get more work done in parallel
I am trying to  understand why striping a FileSystem in a VNX pool increases performance.   Currently, on VNX5300, we mix Block and File in a pool.  To create a filesystem, I will create 1 thick LUN.   Then I create a filesystem and for "Storage Capacity" I give it the exact number of MBs  of the LUN I just created (I check the size with the nas_disk -l command).  This will automatically use a Mapped pool, create 1 disk volume (that maps to the Block LUN I just created),  1 Slice volume, 1 meta volume and the filesystem.   EMC recommended best practice with filesystems is to stripe LUNs that you create your filesystems on.  The explanation is "Stripe volume can achieve greater performance and higher aggregate throughput because all participating  volumes can be active concurrently.  In a stripe volume a read request is made across all component volumes concurrently, happening at the same time."   Because VNX builds volumes on top of Block LUNs, that are striped in 1GB slices across a pool of private RAID groups (and with INYO rebalance those slices based on heat map) the data is well distributed across a lot of spindles.  So the reason for the stripe best practice is not disk utilization.  Is The reason for the striping concurrency?  If a read request is made on a single slice volume, then the read request would be done sequentially.   The block LUN I initially create will write my LUN in 1 GB slices all over the storage pool private RAID groups.  But since it is written to just 1 LUN, the celerra will read the first 1 GB slice, then another 1GB slice, then another, etc.  sequentially.    But if I created a stripe volume, then it is reading smaller stripes concurrently from all the volumes.   I am assuming that with the Slice volume, the celerra cannot read concurrently, because  the celerra thinks that it is only working with 1 slice volume.   But if the celerra thinks it is working with a stripe volume, then it will read concurrently.   Am understanding this correctly?   And Does this provide a big performance increase? 
Trying to understand why striping a Filesystem in a VNX pool increases 
performance