What is vMSC?

vSphere Metro Storage Cluster (vMSC) is a tested and supported configuration for stretched storage cluster architectures. A vMSC configuration is designed to maintain data availability beyond a single physical or logical site. All supported storage devices are listed on either the VMware Storage Compatibility Guide or the Partner Verified and Supported Products (PVSP) listings.

What is HPE 3PAR Peer Persistence?

HPE 3PAR Peer Persistence is an extension of HPE 3PAR Remote Copy software and HPE 3PAR OS that enables a pair of HPE 3PAR StoreServ Storage systems, located at metropolitan distances, to act as peers to each other and present a nearly continuous storage system to hosts connected to them. Volumes presented to hosts are replicated across the pair of arrays and kept in sync. Each pair of replicated and synchronized volumes across each array share the same WWN and appear as the same volume to the hosts. Taking advantage of Asymmetric Logical Unit Access (ALUA) capabilities that allow paths to a SCSI device to be marked as having different characteristics, hosts connect to volumes on one array via active paths, and connect to replicated volumes on the other array via standby paths. ALUA Path status and host availability to the volumes is controlled by Peer Persistence software. This capability allows customers to configure a high-availability (HA) solution between two sites or datacenters where switchover, failover and switchback of access to the volumes across arrays remains transparent to the hosts and applications running on those hosts.

HPE 3PAR Quorum Witness

The HPE 3PAR Quorum Witness is a component provisioned as a virtual machine that is typically deployed at a third site. The HPE 3PAR Quorum Witness, along with the two HPE 3PAR StoreServ Storage systems, forms a three part quorum system. This quorum system allows monitoring of the status of both the HPE 3PAR StoreServ Storage systems and the storage site inter-links. A number of site and inter-link failure scenarios can be recognized by this three part quorum system, and appropriate failover actions implemented. In the event of a disaster that may bring either one of the storage systems or sites down and in conjunction with Peer Persistence software, a failover to the surviving StoreServ system is automatically initiated. During this failover operation, replicated volumes on the remaining storage system are made active. The host paths to those volumes are also made active, thereby ensuring that hosts can continue to access their volumes without any disruption or outage. Communication between the three sites for quorum is via the Quorum Witness IP and the service management IP’s of the two HPE 3PAR StoreServ Storage systems. HPE 3PAR Quorum Witness does not actively participate in data storage and a failure or removal of the HPE 3PAR Quorum Witness from an otherwise functioning environment will have no impact. The HPE 3PAR Quorum Witness only comes into play when one site or the ISL has failed or if two quorum members have failed simultaneously.

Configuration Requirements

These requirements must be satisfied to support a vMSC configuration with HPE 3PAR.

• VMware ESXi 5.0 or higher, Metro Storage Cluster configured for uniform host access per VMware requirements and best practices. 
• HPE 3PAR StoreServ Storage arrays configured for Peer Persistence with Automated Transparent Failover per HPE 3PAR Remote Copy Software User's Guide and Implementing vSphere Metro Storage Cluster using HPE 3PAR Peer Persistence technical white paper. 
  • HPE 3PAR Quorum Witness software must be installed on a virtual machine at a third site. 
  • vSphere vCenter Server connected to ESXi hosts in both datacenters. 
  • Maximum round trip latency on the storage network between sites should not exceed 10ms RTT. 

Note: Updates to the maximum round trip latency specification are published in the HPE 3PAR Support Matrix in the HPE Single Point of Connectivity Knowledge (SPOCK) Storage compatibility matrix. 

• FC-switched, FCoE end-to-end, FCoE to FC switched, and software/hardware iSCSI SAN for host-array connectivity, and array inter-link connectivity setup as remote-copy-over-FC (RCFC) or remote-copy-over IP (RCIP). 
• Any IP subnet used by the virtual machine must be accessible by all ESXi hosts in all data centers within the Metro Storage Cluster. 

Solution Overview

A test qualified VMware Metro Storage Cluster using HPE 3PAR StoreServ Storage is supported in accordance with the VMware description of a uniform access vMSC configuration. Particular to the uniform access configuration, host data path connections at each site are cross-connected to the peer data center site storage array. ESXi hosts access volumes in the data center local array via active paths. Connectivity to standby peer volumes on the distance array is maintained in standby mode until such time as a failover or switchover. In concert with HPE 3PAR Peer Persistence, HPE 3PAR Quorum Witness and with Automated Transparent Failover (ATF) enabled, a minimally disruptive switchover or failover of volume access across sites can be achieved.
For example, in case of an array failure on one site (site 1):

1. Loss of quorum is detected by the Quorum Witness and the surviving storage array at site 2. 
2. Peer Persistence software on array at site 2 makes the peer volumes and the cross-connected paths from the hosts on site 1 to the array on site 2, active. 
3. Site 1 hosts, virtual machines, and applications access peer volumes on site 2 and continue normal operation.

Note: The failover is automated with Peer Persistence and ATF, but transparent failback after fault correction is a manual process. 

This diagram depicts a high level overview:

Sample tested scenarios