HP P4000 Multi-Site SAN Notes

*Edited information from P4000 Multi-Site HA/DR Solution Pack user guide

The Multi-Site SAN features enable synchronously and automatically mirroring data between geographic sites.

1: Designing a Multi-Site SAN

Multi-Site clusters can:
Span up to three sites
Span multiple subnets
Have multiple VIPs
Geographical awareness enabled by designating storage systems as members of a particular site.
Synchronously replicated (mirrored) data between sites, based on volume data protection level.
Site information that ensures that data is mirrored between sites for high availability and disaster recovery.
I/O path preferencing, so that application servers connect to storage systems located in the same site.
Failover Manager support for automatic failover/failback in three-site configurations without requiring a physical storage system in the third site.
Failover Manager for quorum management if the network connection between the two sites becomes unavailable.

2: Requirements

A feature key for each storage system in the management group that is also participating in a Multi-Site cluster
All sites must have the same number of storage systems

3: Protection Offered

Common types of data center failures a Multi-Site SAN protects against include:
Site power outage
Site network outage
Site disaster

Data protection level Number of sites supported:
Network RAID-10 → 2 sites supported
Network RAID–10+1 → 3 sites supported
Network RAID–10+2 → 2 sites supported

Network RAID-10+2 offers a level of data protection that enables the Multi-Site SAN to sustain a complete failure at one site and still maintain replicated data at the other site. With Network RAID-10+2 there are four copies of data for the volume on the SAN.

Table → Common configurations of Multi-Site SANs and managers

4: Designing the network for the Multi-Site SAN

Best practices:

Adequate bandwidth – plan for 50 MB/sec of bandwidth for each storage system in each site (example – if each site contains 4 storage systems, then need 200 MB/sec throughput which translates into two Gigabit Ethernet links (125MB/sec) or more.)
Low round-trip latency – in order to not impact disk I/O to the application server, the round-trip latency between the sites must be no more than 2 ms (which implies a theoretical maximum distance between sites of 299km)
Redundant links – have multiple physical connections (media) between the sites for redundancy (the network should be configured so that a link failure does not cause the Multi-Site SAN to go offline.)
Assign servers to sites – avoid high-latency connections by assigning application servers to the site where the server is

Commonly used designs:
Dual redundant links between the sites
Full-mesh triangular (three) redundant links between sites
Hub and spoke central network core with redundant links out to each site
Combination full-mesh core network with triangular (three) links between sites

Using multiple subnets:

Can use multiple subnets with a Multi-Site SAN. Multiple subnets let you have multiple VIPs, one VIP per subnet. The advantage of using multiple VIPs is that you can connect to a volume without having to leave the local subnet. Alternatively, you can assign an application server to a site.

If using multiple subnets within the iSCSI cluster and implementing one subnet per site, can take advantage of the following Multi-Site SAN features:
One Virtual IP address per site – iSCSI discovery sessions are terminated on a storage system that is local to the application server in that site.
Virtual IP addresses are hosted only on storage systems that reside in the same subnet as the VIP
Read and Write I/O requests are forwarded from the application server to a storage system that is in the same site as the server. This ensures that the I/O path is optimal and multiple network hops across the network link between the sites are eliminated.

5: Other considerations

1: Stretched vSphere HA clustering
2: Stretched subnets spanning the sites


  1. this is a very good "copy and paste" note :)


Post a Comment