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geom_fox.4freebsd

Langue: en

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Version: 361905 (ubuntu - 24/10/10)

Section: 4 (Pilotes et protocoles réseau)


BSD mandoc

NAME

geom_fox - GEOM based basic disk multipathing

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.conf5:

 geom_fox_load="YES"
 

DESCRIPTION

The intent of the framework is to provide basic multipathing support to access direct access devices. Basic in the above sentence should be read as: 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 Fx 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 to detect multiple paths. Using this information it creates a unique da#.fox device.

The 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.

The 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)

CAVEATS

The 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, 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 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.

AUTHORS

An -nosplit The 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 .

BUGS

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

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

The examples provided are too FibreChannel-centric.

Il n'y a pas de pile sous MultiDeskOS. Les fonctions ne sont pas encore récursives,
mais le seront par la suite, via des assignations de variables... Ce qui évitera de
devoir créer des pile et d'avoir des stack overflow.
-- Jayce - Les piles sa pu aussi --