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This is the command mhddfs that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator



mhddfs - The driver combines a several mount points into the single one.


mhddfs /dir1,/dir2[,/path/to/dir3] /path/to/mount [-o options]
mhddfs /dir1 dir2,dir3 /mount/point [-o options]
fusermount -u /path/to/mount

fstab record example:
mhddfs#/path/to/dir1,/path/to/dir2 /mnt/point fuse defaults 0 0

mhddfs#/dir1,/dir2,/dir3 /mnt fuse logfile=/var/log/mhddfs.log 0 0


with an -o option1,option2... you can specify some additional options:

specify a file that will contain debug information.

0 - debug messages

1 - info messages

2 - standard (default) messages

a free space size threshold If a drive has the free space less than the threshold specifed
then another drive will be choosen while creating a new file. If all the drives have free
space less than the threshold specified then a drive containing most free space will be

Default value is 4G, minimum value is 100M.

This option accepts suffixes:
[mM] - megabytes

[gG] - gigabytes

[kK] - kilobytes

For an information about the additional options see output of:
mhddfs -h


The file system allows to unite a several mount points (or directories) to the single one.
So a one big filesystem is simulated and this makes it possible to combine a several hard
drives or network file systems. This system is like unionfs but it can choose a drive with
the most of free space, and move the data between drives transparently for the

While writing files they are written to a 1st hdd until the hdd has the free space (see
mlimit option), then they are written on a 2nd hdd, then to 3rd etc.

df will show a total statistics of all filesystems like there is a big one hdd.

If an overflow arises while writing to the hdd1 then a file content already written will
be transferred to a hdd containing enough of free space for a file. The transferring is
processed on-the-fly, fully transparent for the application that is writing. So this
behaviour simulates a big file system.

The filesystems are combined must provide a possibility to get their parameters correctly
(e.g. size of free space). Otherwise the writing failure can occur (but data consistency
will be ok anyway). For example it is a bad idea to combine a several sshfs systems

Please read FUSE documentation for a further conception.


Distributed under GPLv3

Copyright (C) 2008 Dmitry E. Oboukhov <[email protected]>

February 2008 mhddfs(1)

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