Master Server memory

The Master Server keeps the whole metadata structure in RAM. This structure includes every file, directory, symbolic link, socket, and pipe, every name inside a directory, and the chunk table of every file. The disk holds a periodic dump of that structure and the incremental changelogs. Nothing is read back from the disk to answer a client.

The memory of one machine therefore sets the ceiling on how far a cluster can grow. The capacity of the disks does not set it. Both figures that grow with use are held in that memory: the number of objects and the number of chunks.

There is no configured limit on either figure. The Master Server's RAM decides what a cluster can hold, long before the identifier spaces for objects and chunks run out. Requirements for Master Servers calculates the number of gibibytes that a given number of objects needs.

The Master Server measures its own memory use. In the GUI, the Memory Usage section of the Info tab shows the Master Server's memory broken down by structure. The CLI reports the same numbers. Watch this breakdown as a cluster grows, instead of an estimate made once during planning. To learn which structures the breakdown covers and what it does not include, see what metadata holds and what it costs in RAM.