This topic describes the several ways that cluster engines are
connected in SAN File System.
The SAN File System cluster engines connect with each other in three ways:
- Ethernet LAN connections of the engine network interfaces or ports. These
can be the copper interfaces on the motherboard of the xSeries® 345 or fiber
interfaces on the optional fiber GigE card.
- Ethernet LAN connections of the network interfaces on the RSA IIs in each
engine.
- The RS-485 or serial connection between the RSA IIs.
These connections are used in the following ways:
- The Ethernet port in an metadata server engine is used to:
- Communicate with other metadata server nodes. This communication consists
of cluster heartbeats as well as request-response messages that occur as part
of metadata transactions in the metadata server nodes. For example, if a subordinate
metadata server needs some space from a storage pool, it sends a request to
the master metadata server which allocates a partition to the subordinate.
This results in messages going back and forth between the two metadata servers
through their Ethernet ports.
- Enable communication between SAN File System clients and the metadata
servers.
- Send SNMP traps generated by SAN File System.
- The RSA II Ethernet connection is used to:
- Send SNMP traps from the RSA II to the master console.
- Define the KVM of the master console as the console of the metadata server
engine in which the RSA II resides.
- Update the RSA II firmware through its Web interface.
- The RSA II serial connection (RS-485) is used when the SAN File System
administrative agent , running on the metadata servers, requests that the
local RSA II obtain information from a remote RSA II. This flow of information
occurs over the RS-485 connection. This connection is also used for the requests
generated by one metadata server to stop another that is not functioning
properly.
The Ethernet connections use a customer LAN that does not need to be isolated.
For performance reasons, the metadata server engines and the SAN File System
clients should all be on the same subnet; that is, there should be no routers
or gateways in their paths. If you deploy a metadata server cluster on a heavily
loaded IP-network, it is possible that there could be delays in getting heartbeat
traffic across the network. This could result in unnecessary metadata server
fail-overs. A possible solution to situations such as these would be a dedicated
VLAN.