About Replication Gateway tunables
If you are using Resiliency Platform Data Mover to replicate your data across data centers, you have an option to tune some replication parameters to optimize the performance and scalability of the replication.
Resiliency Platform Data Mover replicates data of the protected virtual machines at the source data center to the target data center. This data of the protected virtual machines is called Veritas Replication Set. Replication Gateway is a staging server that aggregates and batches data from multiple Veritas Replication Sets during replication. This data is transmitted in the unit of update sets and all the replication tunables are related to the update set.
What is an update set
To replicate the data from source data center to target data center, the Data Mover driver taps the workload I/Os and sends it to the source Replication Gateway over LAN. The source Replication Gateway implements a data optimization technique (data de-duplication) and creates a set of workload I/Os. This set of workload I/Os collected over a period of time is called an update set. You can change the size of the update set.
The update set is stored on the staging storage disk in its optimized format. While sending this update set over WAN, data optimization (compression) algorithms are used. As a result of this data optimization, the amount of data sent over WAN is much lower than the amount of data processed for replication by the Replication Gateway.
The update sets are periodically created for each protected workload virtual machine. The WAN link is effectively used by sending multiple update sets in parallel. Resiliency Platform Data Mover is resilient to the network and infrastructure faults. In the event of a network fault or Replication Gateway reboot, it does not send any data over WAN. The replication is resumed from the point where it was paused (before faults) using optimized handshake algorithm. In case of an infrastructure fault such as failure of Replication Gateway, the replication can be resumed through another Replication Gateway. In this case, the amount of data needed to be re-sent is equal to the update set lost on the failed Replication Gateway.
Parameters that can be tuned
Following are the three parameters for Replication Gateway that you can tune to optimize the Recovery Point Objective (RPO), replication performance, and scalability:
How replication works with update set, Replication Frequency, and quota per Veritas Replication Set
The staging storage on the Replication Gateway component of Veritas Resiliency Platform consists of two parts:
Following is the sequence in which update sets get created and stored in various areas of Replication Gateway storage:
Factors governing the replication characteristics
The default size of the update set is chosen in such a way that the Replication Gateway gets maximum possible data optimization as well as maximum WAN bandwidth for replication. Following are some of the factors that affect the size of the update set or can be affected when update set size is changed:
When do you need to change the size of the replication tunables
The default size of update set is tuned to solve most of the applications having moderate sizes of the disks and moderate throughput. These values are tuned to achieve service level agreement (RPO/RTO) for the resiliency group.
You may consider changing the size of the update size in the following situations:
Note that changing these values to a value that does not fit your I/O pattern might violate the service level agreement. For example, if the size of the update set is changed to a considerably smaller size and workload I/O rate is very high, the Replication Gateway tries to optimize as much as possible. But if the WAN bandwidth is low, then Replication Gateway may not be able to provide the desired RPO. In such cases, the replication goes into flow control mode. Once enough space is available on the Replication Gateway, replication is automatically resumed.
So, it is expected to have a WAN link with sufficient bandwidth to sustain the workload I/O traffic. Also, to achieve the best optimization possible, keep the update set size to the default value. In cases where workload I/O rate is not high or virtual machine disk size is not large, you can change the size of the update set and set it to a lower value.
If you decrease the size of the update set, the number of virtual machines to be protected increases and vice versa.
Impact of the change
Quota per Veritas Replication Set (Quota-per-CG)
Scale (number of protected virtual machines)
size of update set (Update-set-size)
Performance (Local Deduplication, compression, RPO)
RPO for all the resiliency groups configured on the gateway
The following formulae are used to calculate these tunables.
How to change the size of the update set
You can change the value of all the replication tunables using the Replication Gateway KLISH menu. You can change these tunables at run-time based on the above parameters. Note that you need to have the same size of the parameters on all the peer gateways.
manage> datamover operation modify-quota-size
manage>datamover operation modify-updateset-size
manage>datamover operation modify-replication-frequency
Note: This article is also published at: https://origin-www.veritas.com/support/en_US/article.100044091
You can access Veritas Resiliency Platform documentation at: https://sort.veritas.com/documents?prod=vrp