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+.TH CRUSHTOOL 8
+.SH NAME
+crushtool \- CRUSH map manipulation tool
+.SH SYNOPSIS
+.B crushtool
+( \fB\-d\fI map\fP | \fB\-c\fI map.txt\fP | \fB\-\-build\fI numosds layer1 ...\fP )
+[ \fB\-o\fI outfile\fP [ \fB\-\-clobber\fP ]]
+.SH DESCRIPTION
+.B crushtool
+is a utility that lets you create, compile, and decompile CRUSH map files.
+.PP
+CRUSH is a pseudo-random data distribution algorithm that efficiently maps
+input values (typically data objects) across a heterogeneous, hierarchically
+structured device map.  The algorithm was originally described in detail in
+the following paper (although it has evolved some since then):
+.IP
+http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
+.PP
+The tool has three modes of operation.
+.TP
+\fB\-c\fI map.txt\fP
+will compile a plaintext \fImap.txt\fP into a binary map file.
+.TP
+\fB\-d\fI map\fP
+will take the compiled \fImap\fP and decompile it into a plaintext source file,
+suitable for editing.
+.TP
+\fB\-\-build\fI numosds layer1 ...\fP
+will create a relatively generic map with the given layer structure.  See below for examples.
+.SH OPTIONS
+.TP
+\fB\-o\fI outfile\fP
+will specify the output file.
+.TP
+\fB\-\-clobber\fP
+will allow the tool to overwrite an existing \fIoutfile\fP (it will normally refuse).
+.SH BUILDING A MAP
+The build mode will generate relatively generic hierarchical maps.  The first argument simply
+specifies the number of devices (leaves) in the CRUSH hierarchy.  Each layer describes how the 
+layer (or raw devices) preceeding it should be grouped.
+.PP
+Each \fIlayer\fP consists of
+.IP
+\fIname\fP ( uniform | list | tree | straw ) \fIsize\fP
+.PP
+The first element is the \fIname\fP for the elements in the layer (e.g. "rack").  Each element's
+name will be append a number to the provided \fIname\fP.
+.PP
+The second component is the type of CRUSH bucket.  
+.PP
+The third component is the maximum size of the bucket.  If the size is \fI0\fP, a single bucket
+will be generated that includes everything in the preceeding layer.
+.SH EXAMPLE
+Suppose we have 128 devices, each grouped into shelves with 4 devices each, and 8 shelves per
+rack.  We could create a three level hierarchy with:
+.IP
+crushtool --build 128 shelf uniform 4 rack straw 8 root straw 0 -o map
+.PP
+To adjust the default (generic) mapping rules, we can
+.IP
+crushtool -d map -o map.txt  # decompile
+.IP
+vi map.txt                   # edit
+.IP
+crushtool -c map.txt -o map  # recompile
+.SH AVAILABILITY
+.B crushtool
+is part of the Ceph distributed file system.  Please refer to the Ceph wiki at
+http://ceph.newdream.net/wiki for more information.
+.SH SEE ALSO
+.BR ceph (8),
+.BR osdmaptool (8),
+.BR mkcephfs (8)