ceph/doc/cephfs/createfs.rst

   1 ========================
   2 Create a Ceph filesystem
   3 ========================
   4
   5 Creating pools
   6 ==============
   7
   8 A Ceph filesystem requires at least two RADOS pools, one for data and one for metadata.
   9 When configuring these pools, you might consider:
  10
  11 - Using a higher replication level for the metadata pool, as any data loss in
  12   this pool can render the whole filesystem inaccessible.
  13 - Using lower-latency storage such as SSDs for the metadata pool, as this will
  14   directly affect the observed latency of filesystem operations on clients.
  15 - The data pool used to create the file system is the "default" data pool and
  16   the location for storing all inode backtrace information, used for hard link
  17   management and disaster recovery. For this reason, all inodes created in
  18   CephFS have at least one object in the default data pool. If erasure-coded
  19   pools are planned for the file system, it is usually better to use a
  20   replicated pool for the default data pool to improve small-object write and
  21   read performance for updating backtraces. Separately, another erasure-coded
  22   data pool can be added (see also :ref:`ecpool`) that can be used on an entire
  23   hierarchy of directories and files (see also :ref:`file-layouts`).
  24
  25 Refer to :doc:`/rados/operations/pools` to learn more about managing pools.  For
  26 example, to create two pools with default settings for use with a filesystem, you
  27 might run the following commands:
  28
  29 .. code:: bash
  30
  31     $ ceph osd pool create cephfs_data <pg_num>
  32     $ ceph osd pool create cephfs_metadata <pg_num>
  33
  34 Generally, the metadata pool will have at most a few gigabytes of data. For
  35 this reason, a smaller PG count is usually recommended. 64 or 128 is commonly
  36 used in practice for large clusters.
  37
  38
  39 Creating a filesystem
  40 =====================
  41
  42 Once the pools are created, you may enable the filesystem using the ``fs new`` command:
  43
  44 .. code:: bash
  45
  46     $ ceph fs new <fs_name> <metadata> <data>
  47
  48 For example:
  49
  50 .. code:: bash
  51
  52     $ ceph fs new cephfs cephfs_metadata cephfs_data
  53     $ ceph fs ls
  54     name: cephfs, metadata pool: cephfs_metadata, data pools: [cephfs_data ]
  55
  56 Once a filesystem has been created, your MDS(s) will be able to enter
  57 an *active* state.  For example, in a single MDS system:
  58
  59 .. code:: bash
  60
  61     $ ceph mds stat
  62     cephfs-1/1/1 up {0=a=up:active}
  63
  64 Once the filesystem is created and the MDS is active, you are ready to mount
  65 the filesystem.  If you have created more than one filesystem, you will
  66 choose which to use when mounting.
  67
  68         - `Mount CephFS`_
  69         - `Mount CephFS as FUSE`_
  70
  71 .. _Mount CephFS: ../../cephfs/kernel
  72 .. _Mount CephFS as FUSE: ../../cephfs/fuse
  73
  74 If you have created more than one filesystem, and a client does not
  75 specify a filesystem when mounting, you can control which filesystem
  76 they will see by using the `ceph fs set-default` command.
  77
  78 Using Erasure Coded pools with CephFS
  79 =====================================
  80
  81 You may use Erasure Coded pools as CephFS data pools as long as they have overwrites enabled, which is done as follows:
  82
  83 .. code:: bash
  84
  85     ceph osd pool set my_ec_pool allow_ec_overwrites true
  86
  87 Note that EC overwrites are only supported when using OSDS with the BlueStore backend.
  88
  89 You may not use Erasure Coded pools as CephFS metadata pools, because CephFS metadata is stored using RADOS *OMAP* data structures, which EC pools cannot store.
  90