10 septiembre 2013

Sizing Storage

Once you get a clear idea who-are-who on the complicated I/O latency world (review other two post here and here).....you need to think about the general rules and best practices to sizing storage for your IOPS needs.

GAVG (Guest Average Latency) total latency as seen from vSphere
KAVG (Kernel Average Latency) time an I/O request spent waiting inside the vSphere storage stack.
QAVG (Queue Average latency) time spent waiting in a queue inside the vSphere Storage Stack.

DAVG (Device Average Latency) latency coming from the physical hardware, HBA and Storage device.

Bad performance if:

High Device Latency: Device Average Latency (DAVG) consistently greater than 20 to 30 ms may cause a performance problem for your typical application.
High Kernel Latency: Kernel Average Latency (KAVG) should usually be 0 in an ideal environment, but anything greater than 2 ms may be a performance problem.

And now, what about the storage?

The typical workload show on this picture, is for the most of the virtual machines, but, othre types like DDBB are so different and will need special configuration like dedicated raidgroups, ssd cache pools, etc.

It´s so important when planning and sizing a infrastructure to bear in mind not only the storage, it´s a mix with the raid conf, diskt typs (ssd, sas, sata), the storage protocol (FC, FCoE, iSCSI or NFS), networking and conf (cabling, switch, vlans conf), vmware conf (storage adapters, datastores conf (vmfs, rdm, advanced parameters) and so on.