Hypervisor Attributes
VMware ESXi/ESX 4.1
Windows Server 2008 R2 with Hyper-V
Citrix Xen Server 5.6
CPUs supported
Recent AMD, Intel
Recent AMD, Intel
Recent AMD, Intel
# CPU cores supported
64
64
64
Memory supported
Unlimited
2TB
256GB
I/O devices supported
IDE, SCSI, SAS, SATA, FC, 1Gb
and 10Gb Ethernet, iSCSI, NFS,
FCOE, Infiniband
IDE, SCSI, SAS, SATA, FC, 1Gb
and 10Gb Ethernet, iSCSI, CIFS,
FCOE, Infiniband
IDE, SCSI, SAS, SATA, FC, 1Gb
Ethernet, iSCSI
Memory optimization
Over-commit, transparent page
sharing, ballooning, large memory
pages
Standard Windows Server 2008
features
None
Platform support
Fewer vendors
More vendors
More vendors
Supported storage of guest VMs
Direct, SAN, NAS, iSCSI
Direct, SAN, iSCSI
Direct, SAN, NAS, iSCSI
Number of nodes in a cluster
32 nodes if < 40 VMs per node
16
16
Operating systems supported
Asainux, CentOS, Debian,
FreeBSD, OS/2, Solaris 10, SCO
OpenServer, SCO Unixware,
Windows Server, RHEL, SUSE,
MS-DOS, Netware
Windows Server, Vista, XP, SUSE
Linux
All Microsoft And Linux Platform
# virtual CPUs supported
8
4
4
# guests per host
256 running
192 running
256 running
# Amount virtual memory
255GB
64GB
64GB
Virtual NICs
10
Yes, limit unknown
16
Small Disk Footprint
70 MB disk footprint
(VMware ESXi)
>2GB with Server Core installation
~10GB with full Windows Server installation
1.8GB
OS Independence
No reliance on general purpose operating system
(VMware ESXi)
Relies on Windows 2008 in Parent Partition
Relies on Linux in Dom
management Partition
Hardened Drivers
Optimized with hardware vendors
Generic Windows drivers
Generic Linux Drivers
Advanced Memory Management
Ability to reclaim unused memory, de-duplicate memory pages, compress memory pages
No ability to reclaim unused physical memory, de-duplicate or compress pages
Recently added basic overcommit, but does not adjust memory allocation based on VM usage; no DE duplication or compression of pages
Advanced Storage Management
VMware vStorage VMFS, Storage vMotion
Lacks an integrated cluster file system, no live storage migration
Lacks an integrated cluster file
system, no live storage migration, storage features support very few arrays
High I/O Scalability
Direct driver model
I/O bottleneck in parent OS
I/O bottleneck in Dom0 management OS
Host Resource Management
Network traffic shaping, per-VM resource shares, set quality of service priorities for storage and network I/O
Lacks similar capabilities
Lacks similar capabilities
Performance Enhancements
AMD RVI, Intel EPT large memory pages, universal 8-way vSMP, VMI Para virtualization, VM Direct Path I/O, PV guest SCSI driver
Large memory pages,
4-way vSMP on Windows
2008 and Windows 7 VMs only
No large memory pages, no paravirt guest SCSI device, no direct I/O device support
 
Virtual Security Technology
 
VMware VMsafe™ security API
Nothing comparable
Nothing comparable
Flexible Resource Allocation
Hot add VM vCPUs and memory, VMFS volume grow, hot extend virtual disks, hot add virtual disks
Only hot add virtual disks
Nothing comparable