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+.. _cephfs-top:
+
+==================
+CephFS Top Utility
+==================
+
+CephFS provides `top(1)` like utility to display various Ceph Filesystem metrics
+in realtime. `cephfs-top` is a curses based python script which makes use of `stats`
+plugin in Ceph Manager to fetch (and display) metrics.
+
+Manager Plugin
+==============
+
+Ceph Filesystem clients periodically forward various metrics to Ceph Metadata Servers (MDS)
+which in turn get forwarded to Ceph Manager by MDS rank zero. Each active MDS forward its
+respective set of metrics to MDS rank zero. Metrics are aggergated and forwarded to Ceph
+Manager.
+
+Metrics are divided into two categories - global and per-mds. Global metrics represent
+set of metrics for the filesystem as a whole (e.g., client read latency) whereas per-mds
+metrics are for a particular MDS rank (e.g., number of subtrees handled by an MDS).
+
+.. note:: Currently, only global metrics are tracked.
+
+`stats` plugin is disabled by default and should be enabled via::
+
+  $ ceph mgr module enable stats
+
+Once enabled, Ceph Filesystem metrics can be fetched via::
+
+  $ ceph fs perf stats
+
+The output format is JSON and contains fields as follows:
+
+- `version`: Version of stats output
+- `global_counters`: List of global performance metrics
+- `counters`: List of per-mds performance metrics
+- `client_metadata`: Ceph Filesystem client metadata
+- `global_metrics`: Global performance counters
+- `metrics`: Per-MDS performance counters (currently, empty) and delayed ranks
+
+.. note:: `delayed_ranks` is the set of active MDS ranks that are reporting stale metrics.
+          This can happen in cases such as (temporary) network issue between MDS rank zero
+          and other active MDSs.
+
+Metrics can be fetched for a partcilar client and/or for a set of active MDSs. To fetch metrics
+for a particular client (e.g., for client-id: 1234)::
+
+  $ ceph fs perf stats --client_id=1234
+
+To fetch metrics only for a subset of active MDSs (e.g., MDS rank 1 and 2)::
+
+  $ ceph fs perf stats --mds_rank=1,2
+
+`cephfs-top`
+============
+
+`cephfs-top` utility relies on `stats` plugin to fetch performance metrics and display in
+`top(1)` like format. `cephfs-top` is available as part of `cephfs-top` package.
+
+By default, `cephfs-top` uses `client.fstop` user to connect to a Ceph cluster::
+
+  $ ceph auth get-or-create client.fstop mon 'allow r' mds 'allow r' osd 'allow r' mgr 'allow r'
+  $ cephfs-top
+
+Command-Line Options
+--------------------
+
+To use a non-default user (other than `client.fstop`) use::
+
+  $ cephfs-top --id <name>
+
+By default, `cephfs-top` connects to cluster name `ceph`. To use a non-default cluster name::
+
+  $ cephfs-top --cluster <cluster>
+
+`cephfs-top` refreshes stats every second by default. To chose a different refresh interval use::
+
+  $ cephfs-top -d <seconds>
+
+Interval should be greater or equal to 0.5 second. Fractional seconds are honoured.
+
+Interactive Commands
+--------------------
+
+1. m : Filesystem selection
+      Displays a menu of filesystems for selection.
+
+2. q : Quit
+      Exit the utility if you are at the home screen (All Filesystem Info),
+      otherwise escape back to the home screen.
+
+The metrics display can be scrolled using the Arrow Keys, PgUp/PgDn, Home/End and mouse.
+
+Sample screenshot running `cephfs-top` with 2 filesystems:
+
+.. image:: cephfs-top.png