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Manual Pages  — GEOM_FOX

NAME

geom_fox – GEOM based basic disk multipathing

CONTENTS

SYNOPSIS

To compile this driver into the kernel, place the following line in your kernel configuration file: options GEOM_FOX

Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):

geom_fox_load="YES"

DESCRIPTION

This driver is obsolete. Users are advised to use gmultipath(8) instead. This driver will be removed in FreeBSD 12 .

The intent of the geom_fox framework is to provide basic multipathing support to access direct access devices. Basic in the above sentence should be read as: geom_fox 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.

Without a multipathing driver the FreeBSD kernel would probe the disks multiple times, resulting in the creation of multiple /dev entries for the same underlying physical device. A unique label written in the GEOM label area allows geom_fox to detect multiple paths. Using this information it creates a unique da#.fox device.

The geom_fox device is subsequently used by the FreeBSD kernel to access the disks. Multiple physical access paths ensure that even in case of a path failure the FreeBSD kernel can continue to access the data.

The geom_fox driver will disallow write operations to the underlying devices once the fox device has been opened for writing.

EXAMPLES

SEE ALSO

GEOM(4), geom(8), gmultipath(8)

AUTHORS

The geom_fox driver was written by Poul-Henning Kamp <Mt phk@FreeBSD.org>. This manual page was written by Wilko Bulte <Mt wilko@FreeBSD.org>.

CAVEATS

The geom_fox 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, geom_fox is not able to re-initiate the I/O to an alternative physical path.

You have to be very sure to provide a unique label for each of the geom_fox 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.

BUGS

The geom_fox framework has only seen light testing. There definitely might be dragons here.

The name geom_fox is completely obscure. Just remember that any sly fox has multiple exits from its hole.

The examples provided are too FibreChannel-centric.


GEOM_FOX (4) September 12, 2015

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Please direct any comments about this manual page service to Ben Bullock.

"I liken starting one's computing career with Unix, say as an undergraduate, to being born in East Africa. It is intolerably hot, your body is covered with lice and flies, you are malnourished and you suffer from numerous curable diseases. But, as far as young East Africans can tell, this is simply the natural condition and they live within it. By the time they find out differently, it is too late. They already think that the writing of shell scripts is a natural act."
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