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ddumbfs manual page


ddumbfs [-C] -o <mount options> <mount-point>


ddumbfs mount a ddumbfs filesystem

ddumbfs is a filesystem that performs inline data deduplication. ddumbfs uses the SHA1 or TIGER hash algorithm to compare the blocks of data

The parent-directory is the directory containing the ddfs.cfg file and ddfsroot directory.


-h, --help

Show help message and exit.

-V, --version

print version

-o <opt[,opt...]>

mount options:


parent-directory is the directory where are the ddfs.cfg file and ddfsroot directory. This option is mandatory


num is the number of CPUs to allocate to the pool of writers. Use num=0 to disable the pool and let each process write data itself.

If num>0 this the the number of writer to start. Don’t use value bigger than 2*CPUs.

If num<0 then the formula -num /100*N°CPUs is used.

For example if you have a quad core:

num N° cpus num N° cpus
-25 5*0.25=1 -100 4*1.00=4
-50 4*0.50=2 -150 4*1.50=6

default is -100


Default is to lock the index in memory. This will speed up the filesystem, because access to the index don’t require access to the disk. If the index to too big to stay in memory, the lock will fail but the mount will continue. Read special file /.ddumbfs/stats to get the status of the mounted filesystem.


Enable or disable diretc io access to the Block File. Use of Direct io can give a small performance improvement when Block File is a block device, and often give poor performance when it is a regular file. Default is to enable direct io when the Block File is a block device. The idea is to avoid to pollute the cache with data that will probably be used only once. This is good for file archiving and backups. When blocks are small ( 4k ), disable direct io will increase performance.


num is the disk usage in % above what a reclaim is managed. If disk usage continues to increase then a reclaim is managed every half way up to 100%. Default is 90.


force a filesystem check at startup

Read the fuse documentation for other fuse related options.


Mounting a ddumbfs is very simple:

ddumbfs -o parent=/data/ddfs /ddumbfs

To reclaim free space after file deletion, you have to start the reclaim procedure. Just access the special reclaim file:

cat /ddumbfs/.ddumbfs/reclaim

You can display statistics:

cat /ddumbfs/.ddumbfs/stats

See also

fsckddumbfs(1), mkddumbfs(8), cpddumbfs(1)


Alain Spineux <>