[mhddfs]여러 disk 하나로 mount 하기

FUSE coolness with mhddfs

Posted by alj on 24 May 2010, 11:22 am

Let’s say you have three disks but you wish to share with Samba or NFS clients.

Of course you could just mount the disks on three separate mount points and export those. Or you could mount the three disks on three mount points inside the same directory and export the parent directory. The problem with both solutions is you have to “balance” the data among the disks – and it will make navigating your TViX, WDTV or Popcorn more annoying.

You could use RAID or LVM to handle all this for you. But. What if you already have data on the disks? What happens if one of the disks dies? With RAID0 or LVM your data is gone.

Luckily you can have the best of both worlds: mhddfs

mhddfs is a FUSE plugin that combines data from several directories and present it in one directory. The only downside is that you do not know (or control) where a file is created. Let’s say you combine /dir1, /dir2 and /dir3 under /virtual. Previously you had /dir1/my_content. This is now /virtual/my_content. If you write a file to /virtual/my_content it will not necessarily end up in /dir1/my_content. This also mean you can not predict what data is lost if you lose a disk.

The plugin is available in Ubuntu

$ sudo apt-get install mhddfs

Using it is pretty simple

$ sudo mkdir /export/hest
$ sudo mhddfs /dir1,dir2,dir3 /export/hest
[sudo] password for alj: 
mhddfs: directory '/dir1' added to list
mhddfs: directory '/dir2' added to list
mhddfs: directory '/dir3' added to list
mhddfs: mount to: /export/hest
mhddfs: move size limit 4294967296 bytes

The “move size limit” deserves an explanation:

if 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 choosen.

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

Now you have the combined space of all three disks

/dir1;/dir2;/dir3
                      589G  329G  260G  56% /export/hest

To mount the combined directory during boot, at this to /etc/fstab:

mhddfs#/dir1,/dir2,/dir3 /export/hest fuse defaults,allow_other 0 0

You can export the combined directory using NFS or Samba. If you export the combined directory using NFS you need to add the fsid option in /etc/exports

/export/hest 192.168.1.0/24(fsid=2,ro,sync,crossmnt,no_subtree_check,insecure)

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Filed under Computer, Linux, Ubuntu Tagged Linux, Ubuntu, unix

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4 Comments

1. Thomas says:

   September 30, 2010 at 17:01

   Ok…

   but i cannot mount the exported filesystem /export/hest on the client server! I got the error:

   “Permission denied”.

   And, when i restart the nfs server i got the message:

   “exportfs: Warning: /export/hest does not support NFS export.”

   Reply to this comment
   • alj says:

     October 10, 2010 at 15:15

     Are there any error messages in /var/log/daemon.log or /var/log/messages?

     Reply to this comment
2. Etienne Charlier says:

   January 7, 2012 at 10:26

   Hello,

   I use mhddfs to join the filesystems of 4 disks.

   the mhddfs created in /etc/fstab

   unfortunately, once a while, the real filesystems are checked for errors ( fsck).
   the mhddfs mount fails because it starts before the fsck end.

   My server ( headless) hangs waiting for a ctrl-d.

   Do you have a solution ?
   Kind regards
   Etienne

   Reply to this comment
3. Frank says:

   March 12, 2012 at 03:41

   Put it in rclocal or as a service late in the boot process