cephfs(8) - Linux man page

Name

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 file 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 stripes per object

-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

Limitations

When setting layout data, the specified stripe unit and stripe count must multiply to the size of an object. 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 is allowed but is not recommended since it can dramatically unbalance your storage cluster's space utilization.

Availability

cephfs is part of the Ceph distributed file system. Please refer to the Ceph documentation at http://ceph.com/docs for more information.

See Also

ceph(8)

Copyright

2012, Inktank Storage, Inc.