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