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Samba HowTo Guide
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Warning

THIS IS NOT A BACKUP, ARCHIVAL, OR VERSION CONTROL SOLUTION!

With Samba or Windows servers, shadow_copy is designed to be an end-user tool only. It does not replace or enhance your backup and archival solutions and should in no way be considered as such. Additionally, if you need version control, implement a version control system. You have been warned.

The shadow_copy module allows you to setup functionality that is similar to MS shadow copy services. When setup properly, this module allows Microsoft shadow copy clients to browse "shadow copies" on Samba shares. You will need to install the shadow copy client. You can get the MS shadow copy client here.. Note the additional requirements for pre-Windows XP clients. I did not test this functionality with any pre-Windows XP clients. You should be able to get more information about MS Shadow Copy from the Microsoft's site.

The shadow_copy VFS module requires some underlying file system setup with some sort of Logical Volume Manager (LVM) such as LVM1, LVM2, or EVMS. Setting up LVM is beyond the scope of this document; however, we will outline the steps we took to test this functionality for example purposes only. You need to make sure the LVM implementation you choose to deploy is ready for production. Make sure you do plenty of tests.

Here are some common resources for LVM and EVMS:

Shadow Copy Setup

At the time of this writing, not much testing has been done. I tested the shadow copy VFS module with a specific scenario which was not deployed in a production environment, but more as a proof of concept. The scenario involved a Samba-3 file server on Debian Sarge with an XFS file system and LVM1. I do NOT recommend you use this as a solution without doing your own due diligence with regard to all the components presented here. That said, following is an basic outline of how I got things going.

  1. Installed Operating System . In my tests, I used Debian Sarge (i.e., testing) on an XFS file system. Setting up the OS is a bit beyond the scope of this document. It is assumed that you have a working OS capable of running Samba.

  2. Install & Configure Samba. See the installation section of this HOWTO for more detail on this. It doesn't matter if it is a Domain Controller or Member File Server, but it is assumed that you have a working Samba 3.0.3 or later server running.

  3. Install & Configure LVM. Before you can make shadow copies available to the client, you have to create the shadow copies. This is done by taking some sort of file system snapshot. Snapshots are a typical feature of Logical Volume Managers such as LVM, so we first need to have that setup.

    The following is provided as an example and will be most helpful for Debian users. Again, this was tested using the "testing" or "Sarge" distribution.

    • Install lvm10 and devfsd packages if you have not done so already. On Debian systems, you are warned of the interaction of devfs and lvm1 which requires the use of devfs filenames. Running apt-get update && apt-get install lvm10 devfsd xfsprogs should do the trick for this example.

    • Now you need to create a volume. You will need to create a partition (or partitions) to add to your volume. Use your favorite partitioning tool (e.g., Linux fdisk, cfdisk, etc.). The partition type should be set to 0x8e for "Linux LVM." In this example, we will use /dev/hdb1.

      Once you have the Linux LVM partition (type 0x8e), you can run a series of commands to create the LVM volume. You can use several disks and/or partitions, but we will use only one in this example. You may also need to load the kernel module with something like modprobe lvm-mod and set your system up to load it on reboot by adding it to (/etc/modules).

    • Create the physical volume with pvcreate /dev/hdb1

    • Create the volume group and add /dev/hda1 to it with vgcreate shadowvol /dev/hdb1

      You can use vgdisplay to review information about the volume group.

    • Now you can create the logical volume with something like lvcreate -L400M -nsh_test shadowvol

      This creates the logical volume of 400 MBs named "sh_test" in the volume group we created called shadowvol. If everything is working so far, you should see them in /dev/shadowvol.

    • Now we should be ready to format the logical volume we named sh_test with mkfs.xfs /dev/shadowvol/sh_test

      You can format the logical volume with any file system you choose, but make sure to use one that allows you to take advantage of the additional features of LVM such as freezing, resizing, and growing your file systems.

      Now we have an LVM volume where we can play with the shadow_copy VFS module.

    • Now we need to prepare the directory with something like

      root#  mkdir -p /data/shadow_share
      

      or whatever you want to name your shadow copy-enabled Samba share. Make sure you set the permissions so that you can use it. If in doubt, use chmod 777 /data/shadow_share and tighten the permissions once you get things working.

    • Mount the LVM volume using something like mount /dev/shadowvol/sh_test /data/shadow_share

      You may also want to edit your /etc/fstab so that this partition mounts during the system boot.

  4. Install & Configure the shadow_copy VFS Module. Finally we get to the actual shadow_copy VFS module. The shadow_copy VFS module should be available in Samba 3.0.3 and higher. The smb.conf configuration is pretty standard. Here is our example of a share configured with the shadow_copy VFS module:

    Example22.3.Share With shadow_copy VFS

    [shadow_share]
    comment = Shadow Copy Enabled Share
    path = /data/shadow_share
    vfs objects = shadow_copy
    writeable = yes
    browseable = yes
  5. Create Snapshots and Make Them Available to shadow_copy.so. Before you can browse the shadow copies, you must create them and mount them. This will most likely be done with a script that runs as a cron job. With this particular solution, the shadow_copy VFS module is used to browse LVM snapshots. Those snapshots are not created by the module. They are not made available by the module either. This module allows the shadow copy-enabled client to browse the snapshots you take and make available.

    Here is a simple script used to create and mount the snapshots:

    #!/bin/bash
    # This is a test, this is only a test
    SNAPNAME=`date +%Y.%m.%d-%H.%M.%S`
    xfs_freeze -f /data/shadow_share/
    lvcreate -L10M -s -n $SNAPNAME /dev/shadowvol/sh_test
    xfs_freeze -u /data/shadow_share/
    mkdir /data/shadow_share/@GMT-$SNAPNAME
    mount /dev/shadowvol/$SNAPNAME \
           /data/shadow_share/@GMT-$SNAPNAME -onouuid,ro
    

    Note that the script does not handle other things like remounting snapshots on reboot.

  6. Test From Client. To test, you will need to install the shadow copy client which you can obtain from the Microsoft web site. I only tested this with an XP client so your results may vary with other pre-XP clients. Once installed, with your XP client you can right-click on specific files or in the empty space of the shadow_share and view the "properties." If anything has changed, then you will see it on the "Previous Versions" tab of the properties window.

Samba HowTo Guide
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