The best storage area network design for a customer will take into consideration a number of critical issues:
- Uptime and availability
- Capacity and scalability
- Replication and disaster recovery
Find out how each of these factors will influence storage area network design choices.
Uptime and availability
Because several servers will rely on a SAN for all of their data, it's important to make the system very reliable and eliminate any single points of failure. Most SAN hardware vendors offer redundancy within each unit like dual power supplies, internal controllers and emergency batteries.
In a typical storage area network design, each storage device connects to a switch that then connects to the servers that need to access the data. To make sure this path isn't a point of failure, the client should buy two switches for the SAN network. Each storage unit should connect to both switches, as should each server. If either path fails, software can failover to the other. Some programs will handle that failover automatically, but cheaper software may require you to enable the failover manually.
Capacity and scalability
A good storage area network design should not only accommodate the client's current storage needs, but it should also be scalable so that the client can upgrade the SAN as needed throughout the expected lifespan of the system.
Because a SAN's switch connects storage devices on one side and servers on the other, its number of ports can affect both storage capacity and speed. By allowing enough ports to support multiple, simultaneous connections to each server, switches can multiply the bandwidth to servers. On the storage device side, enough ports for redundant connections to existing storage units, as well as units to add later should be present.
With several servers able to share the same physical hardware, the security plays an important role in a storage area network design.
Most of this security work is done at the SAN's switch level. Zoning allows giving only specific Servers access to certain LUNs, like a firewall allows communication on specific ports for a given IP address. If any outward-facing application needs to access the SAN, like a website, the switch should be configured so that only the server's IP address can access it.
Replication and disaster recovery
With so much data stored on a SAN, the client wants to build disaster recovery into the system. SANs can be set up to automatically mirror data to another site, which could be a failsafe SAN a few meters away or a disaster recovery (DR) site hundreds or thousands of miles away.
If client wants to build mirroring into the storage area network design, one of the first considerations is whether to replicate synchronously or asynchronously. Synchronous mirroring means that as data is written to the primary SAN, each change is sent to the secondary and must be acknowledged before the next write can happen. The alternative is to asynchronously mirror changes to the secondary site. This replication can be configured to happen as quickly as every second, or every few minutes or hours. This means that the client could permanently lose some data, if the primary SAN goes down before it has a chance to copy its data to the secondary.