Multiple fsnameservers Hosts and Redundant Metadata Networks

The addition of name server hosts to the configuration will increase the amount of name server traffic on the metadata network. Using a redundant metadata network with multi-homed name servers further increases the load.

To help you weigh the benefits versus disadvantages of having multiple name server hosts and redundant meta-data networks, here are some points to consider:

  • The fsnameservers file must be the same for all s.
  • Metadata controllers needn’t be name servers.
  • Each additional fsnameservers entry adds additional heartbeats from every file system host.
  • If multiple metadata networks service an individual file system, each network must have an fsnameservers interface. Each fsnameservers host must have network interface(s) on every metadata network, and each interface must be listed in the fsnameservers file.
  • At maximum heartbeat rate, a host sends a heartbeat message to every fsnameservers entry twice per second. The maximum rate is in effect on a given host when StorNext services are first started, and during transition periods when an FSM is starting or failing over. Thirty seconds after services are started and when a cluster is stable, non-hosts reduce their heartbeat rate to once every 5 seconds.
  • Each heartbeat results in a heartbeat reply back to the sender.
  • The size of the heartbeat and reply message depends on the number of file systems in the cluster.

The following section may help you understand how to calculate computing requirements for name server traffic in a cluster. This example assumes a transition period when all hosts are sending heartbeat messages at twice a second.

  1. Every host sends a heartbeat packet to every name server address, twice per second. If the host is an , the heartbeat packet contains a list of FSMs running locally.
  2. Each name server maintains the master list of FSMs in the cluster. The heartbeat reply contains the list of all FSMs in the cluster.
  3. The NSS packet is 72 bytes, plus the file system entries. Each file system entry is 24 bytes plus the name of the file system (one byte per character), including a zero byte to terminate the string.

The file system name is always rounded up to the next 8-byte boundary. For example, a file system name of 7 characters or less would be rounded up to 8 bytes, and a file system name with 8-15 characters would be rounded up to 16 bytes. If there is room in the packet, a list of file systems which are mounted, or could be mounted, is also included.

  1. The heartbeat message size from non- clients is small because there are no locally running FSMs. The heartbeat reply message size is significant because it contains file system locations for all FSMs in the cluster.
  2. The maximum name server packet size is 63KB (64512). This allows up to 1611 FSMs with names of 7 characters or less. With file system names of 8-15 characters, the maximum packet can hold entries for 1342 FSMs. In configurations where the maximum packet size is reached, each host would receive 129024 bytes per second from each address in the fsnameservers file. This is roughly 1MBit per second per host/address. In a configuration with dual multi-homed name servers, there would be 4 addresses in the fsnameservers file. Each host would then receive 4 Mbits per second of heartbeat reply data at the maximum heartbeat rate (twice a second).
  3. A large cluster with 500 hosts, 1600 FSMs and 4 fsnameservers addresses would produce an aggregate of about 500*4 or 2000 Mbits or 2 Gbits of heartbeat reply messages per second. If the 4 fsnameservers addresses belonged to two nameservers, each server would be generating 1 Gbit of heartbeat reply messages per second.

Note: During stable periods, the heartbeat rate for non- hosts decreases to one tenth of this rate, reducing the heartbeat reply rate by an equivalent factor.

  1. The metadata network carries more than just name server traffic. All metadata operations such as open, allocate space, and so on use the metadata network. File system data is often carried on the metadata network when LAN clients and servers are configured. Network capacity must include all uses of these networks.