1ab3783e1a
bottom of the manpages and order them consistently. GNU groff doesn't care about the ordering, and doesn't even mention CAVEATS and SECURITY CONSIDERATIONS as common sections and where to put them. Found by: mdocml lint run Reviewed by: ru
216 lines
5.8 KiB
Groff
216 lines
5.8 KiB
Groff
.\"
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.\" Copyright (c) 2006 Wilko Bulte
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 2, 2005
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.Dt GEOM_FOX 4
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.Os
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.Sh NAME
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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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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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framework is to provide basic multipathing support to access direct
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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 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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.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.
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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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device is subsequently used by the
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.Fx
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kernel to access the disks.
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Multiple physical access paths ensure that even in case of a path failure the
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.Fx
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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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fox device has been opened for writing.
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.Sh EXAMPLES
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.Pp
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.Bl -bullet -compact
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.It
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.Nm
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needs a label on the disk as follows in order to work properly:
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.Bd -literal
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"0123456789abcdef0123456789abcdef"
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"GEOM::FOX <--unique--id-->"
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.Ed
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.Pp
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For the unique ID 16 bytes are available.
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The
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.Dq Li GEOM::FOX
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is the magic to mark a
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.Nm
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device.
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.Pp
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The actual labelling is accomplished by
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.Bd -literal
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echo "GEOM::FOX someid" | dd of=/dev/da2 conv=sync
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.Ed
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.Pp
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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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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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.Bd -literal
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isp1: Target 1 (Loop 0x1) Port ID 0xe8 (role Target) Arrived
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Port WWN 0x21000004cfc8aca2
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Node WWN 0x20000004cfc8aca2
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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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echo "GEOM::FOX 20000004cfc8aca2" | dd of=/dev/da2 conv=sync
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.Ed
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.Pp
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For non-FibreChannel devices you could for example use the serial
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number of the device.
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Regardless of what you use, make sure the label is unique.
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.Pp
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Once the labelling has been performed and assuming the
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.Nm
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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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Creating new fox (da2)
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fox da2.fox lock 0xfffffc0000fdba20
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.Ed
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.Pp
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.It
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To check which physical devices match a given
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.Nm
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device:
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.Bd -literal -offset indent
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# geom fox list
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Geom name: da2.fox
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Providers:
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1. Name: da2.fox
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Mediasize: 73407865344 (68G)
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Sectorsize: 512
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Mode: r0w0e0
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Consumers:
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1. Name: da2
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Mediasize: 73407865856 (68G)
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Sectorsize: 512
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Mode: r0w0e0
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2. Name: da6
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Mediasize: 73407865856 (68G)
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Sectorsize: 512
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Mode: r0w0e0
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.Ed
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.Pp
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.It
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To check the status of the
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.Nm
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components:
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.Bd -literal
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# geom fox status
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Name Status Components
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da2.fox N/A da2
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da6
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.Ed
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.El
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.Sh SEE ALSO
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.Xr GEOM 4 ,
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.Xr geom 8 ,
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.Xr gmultipath 8
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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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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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.An "Wilko Bulte" Aq wilko@FreeBSD.org .
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.Sh CAVEATS
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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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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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.Nm
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devices.
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Safety belts are not provided.
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For FibreChannel devices it is suggested to use the Port WWN of the device.
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The World Wide Name is guaranteed to be worldwide unique per the
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FibreChannel standard.
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.Sh BUGS
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The
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.Nm
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framework has only seen light testing.
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There definitely might be dragons here.
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.Pp
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The name
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.Nm
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is completely obscure.
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Just remember that any sly fox has multiple exits from its hole.
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.Pp
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The examples provided are too FibreChannel-centric.
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