Hardware

What machine to buy for each role. The counts that these pages use come from sizing the cluster.

The smallest production setup is one Master Server, two Chunkservers, and one client machine. Two Chunkservers are the minimum because a second copy of the data needs a second machine. A Metalogger added to that setup keeps a copy of the metadata on another machine. A Metalogger is the recommended protection for the Master Server. For testing, a cluster can be started on fewer machines, in a non-replicated, single-node configuration. Such a setup is not meant for production. In MooseFS PRO, the recommended minimum is higher PRO (PRO Edition only): at least two Master Servers in a High Availability configuration, and at least three Chunkservers. The High Availability configuration keeps the cluster running when the Leader is offline. Nothing refuses to start with two Chunkservers. However, a Master Server holds the Leader role only as long as fewer than half of the registered Chunkservers are disconnected. With two Chunkservers registered, the loss of one therefore leaves the instance with no Leader, whatever the Master Servers are doing. Leader election and quorum covers the count.

Master Servers covers the machine whose memory holds the metadata. Chunkservers covers the machines that hold the data and the disks to put in them. Metaloggers covers the machine that keeps the spare copy of the metadata. Client machines covers what a mount needs from the host that it runs on. Mixing hardware covers how far the machines may differ from one another.