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33 .Nd "GEOM based basic disk multipathing"
35 To compile this driver into the kernel,
36 place the following line in your
37 kernel configuration file:
38 .Bd -ragged -offset indent
39 .Cd "options GEOM_FOX"
42 Alternatively, to load the driver as a
43 module at boot time, place the following line in
45 .Bd -literal -offset indent
51 framework is to provide basic multipathing support to access direct
53 Basic in the above sentence should be read as:
55 only provides path failover functionality, not load balancing over
56 the available paths etc.
57 Using suitable hardware like SCSI or FibreChannel disks it is
58 possible to have multiple (typically 2) host bus adapters access
59 the same physical disk drive.
61 Without a multipathing driver the
63 kernel would probe the disks multiple times, resulting in the creation of
66 entries for the same underlying physical device.
67 A unique label written in the GEOM label area allows
69 to detect multiple paths.
70 Using this information it creates a unique
76 device is subsequently used by the
78 kernel to access the disks.
79 Multiple physical access paths ensure that even in case of a path failure the
81 kernel can continue to access the data.
85 driver will disallow write operations to the underlying devices once the
86 fox device has been opened for writing.
91 needs a label on the disk as follows in order to work properly:
93 "0123456789abcdef0123456789abcdef"
94 "GEOM::FOX <--unique--id-->"
97 For the unique ID 16 bytes are available.
100 is the magic to mark a
104 The actual labelling is accomplished by
106 echo "GEOM::FOX someid" | dd of=/dev/da2 conv=sync
109 For FibreChannel devices it is suggested to use the Node World Wide
110 Name (Node WWN) as this is guaranteed by the FibreChannel standard to
112 The use of the Port WWN not recommended as each port of a given
113 device has a different WWN, thereby confusing things.
115 The Node WWN can be obtained from a verbose boot as in for example
117 isp1: Target 1 (Loop 0x1) Port ID 0xe8 (role Target) Arrived
118 Port WWN 0x21000004cfc8aca2
119 Node WWN 0x20000004cfc8aca2
122 This Node WWN would then be used like so:
124 echo "GEOM::FOX 20000004cfc8aca2" | dd of=/dev/da2 conv=sync
127 For non-FibreChannel devices you could for example use the serial
128 number of the device.
129 Regardless of what you use, make sure the label is unique.
131 Once the labelling has been performed and assuming the
133 module is loaded the kernel will inform you that it has found a new
135 device with a message similar to
137 Creating new fox (da2)
138 fox da2.fox lock 0xfffffc0000fdba20
142 To check which physical devices match a given
145 .Bd -literal -offset indent
150 Mediasize: 73407865344 (68G)
155 Mediasize: 73407865856 (68G)
159 Mediasize: 73407865856 (68G)
165 To check the status of the
170 Name Status Components
183 driver was written by
184 .An "Poul-Henning Kamp" Aq phk@FreeBSD.org .
185 This manual page was written by
186 .An "Wilko Bulte" Aq wilko@FreeBSD.org .
190 driver depends on the underlying hardware drivers to do the right thing in case
192 If for example a hardware driver continues to retry forever,
194 is not able to re-initiate the I/O to an alternative physical path.
196 You have to be very sure to provide a unique label for each of the
199 Safety belts are not provided.
200 For FibreChannel devices it is suggested to use the Port WWN of the device.
201 The World Wide Name is guaranteed to be worldwide unique per the
202 FibreChannel standard.
206 framework has only seen light testing.
207 There definitely might be dragons here.
211 is completely obscure.
212 Just remember that any sly fox has multiple exits from its hole.
214 The examples provided are too FibreChannel-centric.