MFC: rev. 1.2
- Convert to new SYNOPSIS layout - New Sentence, new line - Remove eol whitespace
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@ -32,7 +32,19 @@
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.Nm geom_fox
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.Nd "GEOM based basic disk multipathing"
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.Sh SYNOPSIS
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.Cd "kldload geom_fox"
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To compile this driver into the kernel,
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place the following line in your
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kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "options GEOM_FOX"
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.Ed
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.Pp
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Alternatively, to load the driver as a
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module at boot time, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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geom_fox_load="YES"
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.Ed
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.Sh DESCRIPTION
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The intent of the
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.Nm
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@ -41,25 +53,26 @@ access devices.
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Basic in the above sentence should be read as:
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.Nm
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only provides path failover functionality, not load balancing over
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the available paths etc.
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Using suitable hardware like SCSI or FibreChannel disks it is
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possible to have multiple (typically 2) host bus adapters access
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the available paths etc.
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Using suitable hardware like SCSI or FibreChannel disks it is
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possible to have multiple (typically 2) host bus adapters access
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the same physical disk drive.
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.Pp
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Without a multipathing driver the
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.Fx
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kernel would probe the disks multiple times, resulting in the creation of
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multiple
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multiple
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.Pa /dev
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entries for the same underlying physical device.
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A unique label written in the GEOM label area allows
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.Nm
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to detect multiple paths. Using this information it creates a unique
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.Nm
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to detect multiple paths.
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Using this information it creates a unique
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.Pa da#.fox
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device.
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.Pp
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The
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.Nm
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The
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.Nm
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device is subsequently used by the
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.Fx
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kernel to access the disks.
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@ -68,8 +81,8 @@ Multiple physical access paths ensure that even in case of a path failure the
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kernel can continue to access the data.
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.Pp
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The
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.Nm
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driver will disallow write operations to the underlying devices once the
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.Nm
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driver will disallow write operations to the underlying devices once the
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fox device has been opened for writing.
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.Sh EXAMPLES
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.Pp
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@ -97,7 +110,7 @@ echo "GEOM::FOX someid" | dd of=/dev/da2 conv=sync
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For FibreChannel devices it is suggested to use the Node World Wide
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Name (Node WWN) as this is guaranteed by the FibreChannel standard to
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be worldwide unique.
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The use of the Port WWN not recommended as each port of a given
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The use of the Port WWN not recommended as each port of a given
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device has a different WWN, thereby confusing things.
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.Pp
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The Node WWN can be obtained from a verbose boot as in for example
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@ -108,7 +121,7 @@ isp1: Target 1 (Loop 0x1) Port ID 0xe8 (role Target) Arrived
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.Ed
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.Pp
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This Node WWN would then be used like so:
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.Bd -literal
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.Bd -literal
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echo "GEOM::FOX 20000004cfc8aca2" | dd of=/dev/da2 conv=sync
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.Ed
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.Pp
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@ -121,7 +134,7 @@ Once the labelling has been performed and assuming the
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module is loaded the kernel will inform you that it has found a new
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.Nm
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device with a message similar to
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.Bd -literal
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.Bd -literal
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Creating new fox (da2)
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fox da2.fox lock 0xfffffc0000fdba20
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.Ed
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@ -164,12 +177,12 @@ da2.fox N/A da2
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.Xr GEOM 4 ,
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.Xr geom 8
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.Sh CAVEATS
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The
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.Nm
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The
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.Nm
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driver depends on the underlying hardware drivers to do the right thing in case
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of a path failure.
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If for example a hardware driver continues to retry forever,
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.Nm
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.Nm
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is not able to re-initiate the I/O to an alternative physical path.
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.Pp
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You have to be very sure to provide a unique label for each of the
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@ -194,8 +207,8 @@ The examples provided are too FibreChannel-centric.
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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.Nm
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driver was written by
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.An "Poul-Henning Kamp" Aq phk@FreeBSD.org .
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This manual page was written by
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This manual page was written by
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.An "Wilko Bulte" Aq wilko@FreeBSD.org .
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