Figure 5 Combination full-mesh core with triangular links to all sites
1. Full mesh core network
Using multiple subnets
IMPORTANT: Best practice is to use a single subnet in most cases.
You 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. Application servers assigned to a site
connect only to storage systems in the same site. For more information, see (page 5).
If you use multiple subnets within the iSCSI cluster and implement one subnet per site, you 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.
Figure 6 (page 10) shows an example of how the Multi-Site SAN setup maps to subnets, VIPs, and
application servers.
Designing the network for the Multi-Site SAN 9
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