cephfs man page

cephfs — ceph file system options utility


cephfs [ path command options ]


cephfs is a control utility for accessing and manipulating file layout and location data in the Ceph distributed storage system.

Choose one of the following three commands:

  • show_layout View the layout information on a file or directory
  • set_layout Set the layout information on a file or directory
  • show_location View the location information on a file


Your applicable options differ depending on whether you are setting or viewing layout/location.

Viewing options

-l --offset

Specify an offset for which to retrieve location data

Setting options

-u --stripe_unit

Set the size of each stripe

-c --stripe_count

Set the number of objects to stripe across

-s --object_size

Set the size of the objects to stripe across

-p --pool

Set the pool (by numeric value, not name!) to use

-o --osd

Set the preferred OSD to use as the primary (deprecated and ignored)


When setting layout data, the specified object size must evenly divide by the specified stripe unit. Any parameters you don't set explicitly are left at the system defaults.

Obviously setting the layout of a file and a directory means different things. Setting the layout of a file specifies exactly how to place the individual file. This must be done before writing any data to it. Truncating a file does not allow you to change the layout either.

Setting the layout of a directory sets the "default layout", which is used to set the file layouts on any files subsequently created in the directory (or any subdirectory).  Pre-existing files do not have their layouts changed.

You'll notice that the layout information allows you to specify a preferred OSD for placement. This feature is unsupported and ignored in modern versions of the Ceph servers; do not use it.


cephfs is part of Ceph, a massively scalable, open-source, distributed storage system. Please refer to the Ceph documentation at http://ceph.com/docs for more information.

See Also



Apr 17, 2017 dev Ceph