cephfs man page

cephfs — ceph file system options utility

Synopsis

cephfs [ path command options ]

Description

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

Options

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)

Limitations

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.

Availability

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

ceph(8)

Info

Oct 26, 2016 dev Ceph