cephfs is a control utility for accessing and manipulating file layout and location data in the Ceph distributed file system.
Choose one of the following three commands:
Your applicable options differ depending on whether you are setting or viewing layout/location.
Set the size of each stripe
Set the number of objects to stripe across
Set the size of the objects to stripe across
Set the pool (by numeric value, not name!) to use
Set the preferred OSD to use as the primary
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 the Ceph distributed file system. Please refer to the Ceph documentation at http://ceph.com/docs for more information.