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Monthly Archives: October 2013

SAP on VMware Sizing & Design Example

Recently in partner workshops I have come across some interesting discussions about the impact of hyper-threading and NUMA in sizing business critical applications on VMware. So here is an SAP example based on SAP’s sizing metric “SAPS” (a hardware-independent unit of measurement that equates to SAP OLTP throughput of Sales and Distribution users).  The examples here refer to vSphere scheduling concepts in this useful whitepaper The CPU Scheduler in VMware vSphere 5.1 .

SAP sizing requires the SAPS rating of the hardware which for estimation purposes can be obtained from certified SAP benchmarks published at http://www.sap.com/solutions/benchmark/sd2tier.epx . Let’s use certification 2011027  and assume that we plan to deploy on similar hardware as used in this benchmark. This is a virtual benchmark on vSphere 5 with the following result: 25120 SAPS (at ~100% CPU) for 24 vCPUs running on a server with 2 processors, 6 cores per processor and 24 logical CPUs as hyper-threading was enabled. This is a NUMA system where each processor is referred to as a NUMA node.  (Note cert 2011027 is an older benchmark, the SAPS values for vSphere on newer servers with faster processors would be different/higher, hence work with the server vendors to utilize the most recent and accurate SAPS ratings). Continue reading

Setting Multi Writer Flag for Oracle RAC on vSphere without any downtime

Oracle RAC Cluster using ASM for storage would require the shared disks to be accessed by all nodes of the RAC cluster.

The multi-writer option in vSphere allows the VMFS-backed disks to be shared by multiple VM’s simultaneously. By default, the simultaneous multi-writer “protection” is enabled for all .vmdk files ie all VM’s have exclusive access to their .vmdk files. So in order for all of the Oracle RAC VM’s to access the shared vmdk’s , the multi-writer protection needs to be disabled.

KB Article 1034165 provides more details on how to set the multi-writer option manually to allow VM’s to share vmdk’s (link below).

The above method would require the VM’s to be powered off before the multi-writer option can be set in the .vmx configuration file. This means that the Oracle RAC instance would have to be shutdown and the VM completely powered off before the option can be set leading to an Instance outage. Continue reading