Working with Multiple Instances of the MapR-FS

The Multi-MFS feature allows multiple instances of the FileServer to run on a single node in a single process.

Multiple instances of the MapR FileServer can run on a single node in a single process with the installation of MapR-XD or the MapR-DB software. On servers with SSDs with at least 2 storage pools (SP), two instances (per node) are configured by default. On servers without SSDs, a single instance is configured by default. Each instance runs as a separate library that is dynamically loaded into a single process. In this mode, each instance has a separate host ID; however, all of the instances share the same hostname.

File Server Instances

On MapR-XD and MapR-DB installations, nodes with SSDs can run multiple FileServer instances. To determine whether a node has SSDs, MapR uses the value of SSD in /sys/block/<diskname>/queue/rotational file, which must be set to 0.

The CLDB computes the number of FileServer instances on each node based on the number of storage pools and the type of license. For clusters with MapR-DB license, CLDB configures nodes with SSDs to have two FileServer instances by default and for clusters with MapR-XD license, CLDB configures nodes with SSDs to have one FileServer instance by default.

Ports for Multi-MFS

Each instance listens on its own set of ports. Ensure that the ports are open for this feature. For example, instance 0 will use four ports from 5660, 5692 (5660+32), 5724 (5660+64), and 5756 (5660+96), instance 1 will use four ports from 5661, 5693, 5725, 5757, and so on for every additional instance. The topology of all instances is the same.

To verify that these ports are open, run the following command from a remote machine:

mrconfig -i -h <ip> -p <port number> info threads

An error indicates that the port is not open. If a port (for example, port 5661) is blocked, this command will print something similar to the following:

------------------
|From Instance 5661::|
------------------
<...> rpc failed <...>

Log Files

Each instance has its own set of log files in $MAPR_HOME/logs. When multiple instances are configured, the log files have the same name with a different instance ID; for example, mfs.log.<N>-3 where N is the instance number.

Note: For the primary instance, the log file name does not include the instance number.

The RPC and security trace information are in a separate file per instance, mfs-<N>.err, where N is the instance number. For the primary instance, the file name does not include the instance number.

For example, suppose there are 2 instances running on ports 5660 and 5661. There will be 2 sets of log files, one per instance:

  • mfs.log-3 for the primary instance
  • mfs.log.1-3 for the second instance

The RPC and security trace information will be in these files:

  • mfs.err for the primary instance
  • mfs-1.err for the second instance