Potential performance impact for a RHEL or RHEV hypervisor when I enable Virtage on my Hitachi server.

Updated -

Issue

Potential performance impact for a RHEL or RHEV hypervisor when I enable Virtage on my Hitachi server.

Environment

  • Servers using Hitachi Virtage hardware partitioning mechanism with dedicated resources.
  • The use of Hitachi Virtage hardware partitioning mechanism with shared resources running a RHEL or RHEV hypervisor and associated guest operating systems is NOT supported by Red Hat.

Resolution

  • Hitachi offers a hardware partitioning mechanism known as Virtage on its BladeSymphony servers. The logical partitions or LPARs can be configured to run in either dedicated or shared mode for their processor and I/O adapter resources. Red Hat supports a RHEL or RHEV hypervisor in a Virtage LPAR when that partition is configured in dedicated mode, that is, when I/O adapters, processors and memory are dedicated to that specific partition only and RHEL views the hardware transparently through the LPAR firmware.

  • When Virtage defines an LPAR with a dedicated set of I/O adapters, processors and memory, there is still an overhead associated with Virtage's handling of such things as interrupt mapping, buffer manipulations and Intel VT-x2 functions for guest hypervisors available with Intel Xeon 5500 series processor and its follow-on processors. The degree of performance degradation vary with workload types.

  • While this overhead is often small, there are specific workloads that have been observed with as much as a 35% overhead introduced by the use of Hitachi LPARs. This performance degradation is specifically the result of using Virtage LPARs and is not caused by Red Hat Enterprise Linux (RHEL) or Red Hat Enterprise Virtualization (RHEV). Customers concerned with such performance degradation should consult directly with Hitachi.