Assuring Quality of Service


Assuring quality of service makes your storage performance predictable. CloudByte ElastiStor is unique in its QoS offering as it lets you

  • Easily commission storage with guaranteed IOPS at various levels. You can decide to configure QoS at a Pool level, TSM level, or Storage Volume level.
  • Configure multidimensional QoS involving IOPS, throughput, latency, and capacity.
  • Utilize untapped system resources. For example, assume that have three TSMs but only one is active. In this case, the active TSM can use the entire system’s capability.
  • On-demand modification of settings without system restarts.

Choosing your QoS

The following points help you choose an appropriate QoS:

Endpoint: Decide at what level you want to implement QoS.

Select a capable pool: Based on TSM’s requirements, you provision it on a capable Pool that can meet the requirements. Define the pool level QoS, based on Pool configuration and the controller level. QoS is determined based on the Pool capacity, which is the underlying storage capability.

QoS provisioning: Understand your TSM’s QoS requirements across the data access and data protection needs. Based on the requirement of the TSM, you can either choose QoS automatically or manually. Ensure that you are aware of the Pool settings and how effectively you want to use it at the TSM level.

Sub-divide QoS: Within a TSM, based on varying needs, further sub-divide QoS across Storage Volume, based on the guarantee that the administrator wants to set. For example, when a TSM is used to store logs in the database, since logs need higher IOPS and lower throughput and latency, set it accordingly. Whereas a database requires low IOPS, high throughput, and high latency.


Use ElastiCenter to configure QoS settings. The configuration can be at the following levels:

  • Pool: For details,see Creating a Storage pool.
  • Account: For details, see Creating an Account.
  • TSM: For details, see Provisioning TSM.

Configuring Grace

What is Grace

Grace is the provisioning of unused IOPS/throughput of Pools to Storage Volumes based on the performance requirements. You can configure Grace at Pool level and Storage Volume level.

For example, assume that you have a Pool with the capacity of 100 IOPS and Grace enabled. Two TSMs named TSM A and TSM B, with a capacity of 30 IOPS and 60 IOPS respectively are created under the Pool.

  • Under TSM A (with 30 IOPS capacity), Storage Volumes named E and F are created, and assigned 10 IOPS and 15 IOPS respectievely.
  • Under TSM B (with 60 IOPS capacity), Storage Volume G is created and assigned 35 IOPS.
  • The grace available in this scenario is 40 IOPS.

Configuring Grace at the Pool level

Grace is enabled by default at Pool level. You can edit Grace after creating a storage Pool.

  1. Go to the pool page and then in the Actions pane, click Settings
  2. Edit the settings and enable/disable Grace.

Monitoring QoS

QoS monitoring features will be available in the future releases.

QoS tips

Storage capacity

Discs, storage Connectivity, and type

Capability: Ensure that you are well aware of the capabilities of your storage subsystem. For example, the right interconnection between the controller and storage, the type of disks on the disk array, and the ability to expand the capacity.

Limitations: Ensure that you have assessed the limitations. For example, increasing storage capacity does not make any sense if the network does not support.

Controller characteristics

RAM, CPU, and network:

CPU: If the storage is more I/O bound than CPU bound, it is more effective. CPU load should not be more than 60-70 percent, or you add more cores.

RAM: RAM determines the ability to cache. Larger RAM means more filesystem caches. In a READ-centric scenario, larger RAM helps generate better QOS. That is, more I/O and throughput but lesser latency.

Network: Network capacity decides data access and data protection. Assure adequate network bandwidth to export performance to clients. Network should do justice to the storage system.

Segregation: Segregate data access and data protection so that protection workloads do not interfere with data access workloads.

Pool Creation

Storage group tips

As a best practice, create storage with 8 to 10 disks.

When you add storage groups, keep them identical. For example, do not add disparate groups to the same Pool. For example, if a group has SATA disks, and another group has SAS disks, then do not assign both to the same Pool. That is, do not create hybrid Pools.

Multiple Pools within a Controller

Tips to avoid contention points: Be judicious when you add multiple Pools to a controller. For example, it does not make sense if network bandwidth is already utilized to the maximum with the existing Pools, or CPUs are already busy serving the existing Pools. QoS also suffers because of over provisioning.

When to combine multiple pools: When no conflict pertaining to bandwidth, CPU, or Memory exist, you can combine Pools.

Optimizing QoS

Disk characterstics: Better the disk characteristics, better the QOS. For example, the IOPS, throughput, and latency of SATA disks are not as good as that of SS disks.

Disk layout: Better the disk layout, better the QoS. For example, keep the disk layout to 8 to 10 disks.

Improving WRITE performance: If the application requires synchronous WRITES, associate high performing disk to the Pool to speed up the WRITEs. This guarantees better QOS.

Improving READ performance: To improve the READ performance or increase the filesystem cache hit rate, add high performing disks as cache devices to the Pool.