This is where clarity about what is being asked is important. There are two different things you need to think of since there there is logical space and physical space
1.)Both the eseries and fas/ontap systems give you options of grouping the disks. Ontap calls the aggregates and santricity calls them volume groups, this is usually a form of raid
2.)Ontap and eseries lets you create logical seperations as well. In ontap you can create volumes and luns, where multiple luns can be in a volume, but volumes can also be used for NFS or CIFS. In eseries its just one lun per volume.
There can be situations where you want multiple smaller aggregates, I think when there are stronger controller heads, so the cpu can work on more volumes at a time. NetApp has what's call volume affinities, which means basically how many volumes it can work at the same time. This is why at least with netapp its a good to check with them as well, as there are performance considerations that should be made. Again in general I think you can make an entire disk shelf one big aggreate so all the disks can work together, and then do smaller luns to split that bigger aggregate up logically.
Eseries I'm not aware of ther recommendation, but I do the same and everything works pretty well.
