The QoS (Quality of Service), ensures that the required level of storage performance and SLAs are met. StorPool has 2 features in this sections:

1. Fairness between volumes
StorPool has fairness mechanisms on several levels in the stack so it is hard for one VM to affect the performance/latency observed by other VMs. In this way each volume gets a fair share of the performance of the storage system and no one volume can “steal” all of the performance of the entire system.

2. QoS
An user configurable limit of IOPS and MB/s, per volume/LUN (virtual disk of a VM). By using this feature, a particular user can be guaranteed a certain level of service parameters.

The limit is strictly enforced, i.e. if you set a limit of 1000, you get 1000 IOPS exactly from the first second. There’s no bursting possibility at present. The limit can be changed at any time.

Some customers use the IOPS and MB/s limits only to ring-fence outliers and abusers. Other customers limit all volumes to a large IOPS number (e.g. 50,000 IOPS) only to make sure one VM or a small number of VMs are not taking the full capability of the host it is running on (which is circa 200-300k IOPS per host, depending on CPU and network).