VSAN-Troubleshooting-Reference-Manual

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Diagnostics and Troubleshooting Reference Manual – Virtual SAN Backup/restore operations There are two distinctions to be made in this section. Is Virtual SAN being used as a backup target, or is it being used as a destination? VMware supports vSphere Data Protection (VDP) running on Virtual SAN, so it could be that it may not only be a source for VMs that are being backed up, but also a destination for the backups. When backing up virtual machines on a Virtual SAN datastore, one should expect that the initial backup would involve sequential reads for the initial backup. If using VDP on Virtual SAN as a backup store, one should expect there to be a significant amount of sequential writes for the first backup. Subsequent backup operations are incremental, so will only read and write blocks of data that have changed since the last backup. Doing backups and restores during production hours, when other virtual machines are still running, may have an impact on overall performance, depending on how many VMs are being backed up, and/or restored. A recommendation would be to do backup and restore activities like this out-of-hours so as to lessen the impact on the production VMs, although incremental backups have less of an impact when compared to full backups. One additional note of backup and restores; keep in mind is that the VM Storage Policy is not backed up with the VM. This isn’t a problem if you are restoring to the original location and overwriting the existing VM; in this case you maintain the VM Storage Policy when you restore. However, if you restore to an original location and the original VM no longer exists, or if you restore to a new location, the VM will be restored with a default VM Storage Policy (which has NumberOfFailuresToTolerate = 1). Therefore you will need to reapply the VM Storage Policy to this virtual machine after it has been restored. This will lead to a new reconfiguration and resync, and this operation may once again have an impact on production virtual machine I/O. vMotion vMotion operations consume a significant amount of CPU resources and network bandwidth to complete the operation in the shortest time possible. This can inadvertently affect the performance of Virtual SAN if not planned correctly. Guidelines take from a vSphere 5 vMotion Performance Study (http://www.vmware.com/files/pdf/vmotion-perf-vsphere5.pdf) recommend the use of 10Gb NICs, Network I/O Control (NIOC) and setting aside a certain amount of CPU just for vMotion operations. Failure to follow these guidelines could inadvertently impact the performance of Virtual SAN during vMotion operations. The good thing is that Virtual SAN entitles you to the Distributed Switch functionality, no matter which vSphere edition you use with Virtual SAN. This means V M W A R E S T O R A G E B U D O C U M E N T A T I O N / 2 5 6
Diagnostics and Troubleshooting Reference Manual – Virtual SAN that you have NIOC that will allow you to place Quality Of Service (QoS) on vMotion, Virtual SAN and other network traffic types. With this in place, vMotion can run during production hours, and won’t inadvertently impact Virtual SAN operations. Virus Scans From the VMware paper “Antivirus Best Practices for VMware Horizon View 5.x” which can be found here http://www.vmware.com/files/pdf/VMware-View- AntiVirusPractices-TN-EN.pdf, the challenge with Virus Scans is most virus scanning model involves agents executing on every desktop performing antivirus scanning. During these operations, system resource usage can spike or become overly committed. Performance is severely impacted by these “antivirus storms.” Traditional antivirus agents are resource-intensive and antivirus storms can cause 100 percent saturation in the compute and storage (including a Virtual SAN datastore). In addition, the memory footprint is significant when antivirus software is installed on each virtual machine. VMware has solutions to address the “antivirus storm” issue by consolidating and offloading all antivirus operations into one centralized security virtual appliance. The whitepaper referenced above has further information. Notes on using IOmeter with Virtual SAN Many administrators rely on a tool called IOmeter to do storage performance testing. This is also true for performance testing on Virtual SAN. When the results of this testing are not correctly understood, or do not meet expectations, the assumption is that there is an underlying performance issue with Virtual SAN. This is not necessarily the case, and more often than not it is how IOmeter has been configured to run. If the plan is to use IOmeter to test Virtual SAN performance, there are a number of factors that need consideration. 1. Iometer creates synthetic workloads, not reflective of real-life workloads. Real life virtual machine workloads do not behave like synthetic IOmeter workloads. IOmeter workloads tend to be steady state, repeating the same patterns over and over again. Production workloads are typically not like that, with peaks and troughs, as well as bursts of traffic. 2. The working set of a VM running IOmeter can be configured to be much, much larger than a working set of a production VM. IOmeter can consume a whole VMDK as its working set, which is usually not reflective of production workloads. 3. Your cache is limited. When using IOmeter consider the working set and if it fits in cache. Consider a small number of VMs with a large working set V M W A R E S T O R A G E B U D O C U M E N T A T I O N / 2 5 7
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