215 lines
5.8 KiB
Groff
215 lines
5.8 KiB
Groff
.\"
|
|
.\" Copyright (c) 2006 Wilko Bulte
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd January 2, 2005
|
|
.Os
|
|
.Dt GEOM_FOX 4
|
|
.Sh NAME
|
|
.Nm geom_fox
|
|
.Nd "GEOM based basic disk multipathing"
|
|
.Sh SYNOPSIS
|
|
To compile this driver into the kernel,
|
|
place the following line in your
|
|
kernel configuration file:
|
|
.Bd -ragged -offset indent
|
|
.Cd "options GEOM_FOX"
|
|
.Ed
|
|
.Pp
|
|
Alternatively, to load the driver as a
|
|
module at boot time, place the following line in
|
|
.Xr loader.conf 5 :
|
|
.Bd -literal -offset indent
|
|
geom_fox_load="YES"
|
|
.Ed
|
|
.Sh DESCRIPTION
|
|
The intent of the
|
|
.Nm
|
|
framework is to provide basic multipathing support to access direct
|
|
access devices.
|
|
Basic in the above sentence should be read as:
|
|
.Nm
|
|
only provides path failover functionality, not load balancing over
|
|
the available paths etc.
|
|
Using suitable hardware like SCSI or FibreChannel disks it is
|
|
possible to have multiple (typically 2) host bus adapters access
|
|
the same physical disk drive.
|
|
.Pp
|
|
Without a multipathing driver the
|
|
.Fx
|
|
kernel would probe the disks multiple times, resulting in the creation of
|
|
multiple
|
|
.Pa /dev
|
|
entries for the same underlying physical device.
|
|
A unique label written in the GEOM label area allows
|
|
.Nm
|
|
to detect multiple paths.
|
|
Using this information it creates a unique
|
|
.Pa da#.fox
|
|
device.
|
|
.Pp
|
|
The
|
|
.Nm
|
|
device is subsequently used by the
|
|
.Fx
|
|
kernel to access the disks.
|
|
Multiple physical access paths ensure that even in case of a path failure the
|
|
.Fx
|
|
kernel can continue to access the data.
|
|
.Pp
|
|
The
|
|
.Nm
|
|
driver will disallow write operations to the underlying devices once the
|
|
fox device has been opened for writing.
|
|
.Sh EXAMPLES
|
|
.Pp
|
|
.Bl -bullet -compact
|
|
.It
|
|
.Nm
|
|
needs a label on the disk as follows in order to work properly:
|
|
.Bd -literal
|
|
"0123456789abcdef0123456789abcdef"
|
|
"GEOM::FOX <--unique--id-->"
|
|
.Ed
|
|
.Pp
|
|
For the unique ID 16 bytes are available.
|
|
The
|
|
.Li GEOM::FOX
|
|
is the magic to mark a
|
|
.Nm
|
|
device.
|
|
.Pp
|
|
The actual labelling is accomplished by
|
|
.Bd -literal
|
|
echo "GEOM::FOX someid" | dd of=/dev/da2 conv=sync
|
|
.Ed
|
|
.Pp
|
|
For FibreChannel devices it is suggested to use the Node World Wide
|
|
Name (Node WWN) as this is guaranteed by the FibreChannel standard to
|
|
be worldwide unique.
|
|
The use of the Port WWN not recommended as each port of a given
|
|
device has a different WWN, thereby confusing things.
|
|
.Pp
|
|
The Node WWN can be obtained from a verbose boot as in for example
|
|
.Bd -literal
|
|
isp1: Target 1 (Loop 0x1) Port ID 0xe8 (role Target) Arrived
|
|
Port WWN 0x21000004cfc8aca2
|
|
Node WWN 0x20000004cfc8aca2
|
|
.Ed
|
|
.Pp
|
|
This Node WWN would then be used like so:
|
|
.Bd -literal
|
|
echo "GEOM::FOX 20000004cfc8aca2" | dd of=/dev/da2 conv=sync
|
|
.Ed
|
|
.Pp
|
|
For non-FibreChannel devices you could for example use the serial
|
|
number of the device.
|
|
Regardless of what you use, make sure the label is unique.
|
|
.Pp
|
|
Once the labelling has been performed and assuming the
|
|
.Nm
|
|
module is loaded the kernel will inform you that it has found a new
|
|
.Nm
|
|
device with a message similar to
|
|
.Bd -literal
|
|
Creating new fox (da2)
|
|
fox da2.fox lock 0xfffffc0000fdba20
|
|
.Ed
|
|
.Pp
|
|
.It
|
|
To check which physical devices match a given
|
|
.Nm
|
|
device:
|
|
.Bd -literal -offset indent
|
|
# geom fox list
|
|
Geom name: da2.fox
|
|
Providers:
|
|
1. Name: da2.fox
|
|
Mediasize: 73407865344 (68G)
|
|
Sectorsize: 512
|
|
Mode: r0w0e0
|
|
Consumers:
|
|
1. Name: da2
|
|
Mediasize: 73407865856 (68G)
|
|
Sectorsize: 512
|
|
Mode: r0w0e0
|
|
2. Name: da6
|
|
Mediasize: 73407865856 (68G)
|
|
Sectorsize: 512
|
|
Mode: r0w0e0
|
|
.Ed
|
|
.Pp
|
|
.It
|
|
To check the status of the
|
|
.Nm
|
|
components:
|
|
.Bd -literal
|
|
# geom fox status
|
|
Name Status Components
|
|
da2.fox N/A da2
|
|
da6
|
|
.Ed
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr GEOM 4 ,
|
|
.Xr geom 8
|
|
.Sh CAVEATS
|
|
The
|
|
.Nm
|
|
driver depends on the underlying hardware drivers to do the right thing in case
|
|
of a path failure.
|
|
If for example a hardware driver continues to retry forever,
|
|
.Nm
|
|
is not able to re-initiate the I/O to an alternative physical path.
|
|
.Pp
|
|
You have to be very sure to provide a unique label for each of the
|
|
.Nm
|
|
devices.
|
|
Safety belts are not provided.
|
|
For FibreChannel devices it is suggested to use the Port WWN of the device.
|
|
The World Wide Name is guaranteed to be worldwide unique per the
|
|
FibreChannel standard.
|
|
.Sh BUGS
|
|
The
|
|
.Nm
|
|
framework has only seen light testing.
|
|
There definitely might be dragons here.
|
|
.Pp
|
|
The name
|
|
.Nm
|
|
is completely obscure.
|
|
Just remember that any sly fox has multiple exits from its hole.
|
|
.Pp
|
|
The examples provided are too FibreChannel-centric.
|
|
.Sh AUTHORS
|
|
.An -nosplit
|
|
The
|
|
.Nm
|
|
driver was written by
|
|
.An "Poul-Henning Kamp" Aq phk@FreeBSD.org .
|
|
This manual page was written by
|
|
.An "Wilko Bulte" Aq wilko@FreeBSD.org .
|