[Is XenServer 7 an advanced format (512e or 4Kn) aware OS?]

No, AFAIK, not 512e, either. Newer versions of vSphere and VSAN (VMware) do.

-=Tobias

 

Any system that can support 512n drives can support 512e drives. The whole idea of 512e is that a legacy system can use the newer Advanced Format drives. There might a be limit though to the maximum disk size supported on older systems.

Also using AF 512e drives can hurt performance especially with very small IO as for each 512bytes IO the disk will read/write 4096bytes so it those surrounding bytes are not used in the next IO's performance will decrease. Very often though the disk IO will involve many more surrounding bytes and only some performance is wasted. Using 4kn with a compatible OS can help as the OS is aware of the real block size on the disk.

 

When using a NAS with 4kn disks and XenServer there should be no problem as XenServer won't have to deal with the 4kn,

 

So the lack of 4kn support on XenServer only limits locally attached storage

[Nested Hypervisors in Xenserver 7]

Keep in mind that when running a hypervisor under another hypervisor CPU virtualization extensions are not available for the 2nd hypervisor. So you can only run a 2nd hypervisor that is able to work without those virtualization extensions. Xen for instance can do this but it losses certain capabilities that will limit its functionality and lower its speed.

 

There are also some hypervisors that can emulate those CPU virtualization extensions for VM's. So these will provide full fucntionality to the 2nd hypervisor though with reduced performance.

 

So running a hypervisor under another hypervisor is never recommended for production use, there are just too many downsides. For testing it might be fine. (I sometimes run XenServer under Vmware player/Virtualbox on my Windows desktop, to find out if a certain driver is available, or how to make yum install work under XenServer 7.0) For real testing scenarios I keep some old servers and storage devices though.