Shadow copies of shared folders are point-in-time snapshots of a shared folder that are exposed to Windows 2000+ users by way of the "Previous Versions" tab on a shared file.
The shadow copies client is built into Windows 2003 and Windows XP SP1 and above, and available for download for Windows 2000.
Yes, it is supported in Samba by way of a Samba VFS module.
The only source of documentation on setting up Samba to provide shadow copies to Microsoft clients is the Stackable VFS modules section of the Samba HOWTO.
This document will give you a good idea of how to set this all up.
This document is written using Ubuntu Dapper, but you should be able to use the information on any distribution with new enough components.
LVM provides a method for taking a snapshot of a volume; it is these snapshots that will be shared and provided to Windows clients as shadow copies. XFS supports freezing a file system, buffering writes to it until it is thawed again. However, this doesn't actually work right now. Many filesystems in the kernel support waiting until the filesystem is consistent before taking a snapshot - you might wish to research this in more detail, but for this HOWTO we will use XFS.
1. Join a Windows domain, if you need to. I followed this howto, which should be rolled into our wiki, which is a huge mess of conflicting information about joining Windows domains that really needs some Aristotle love.
It's always handy to keep in time with your Windows network, so install ntp-simple and edit /etc/ntp.conf to parent off your AD server.
2. Set up a Samba share to the root of your LVM volume. Unfortunately, shadow copies don't work if you share a directory inside the volume. You can use "deep mounting" on Windows 2000 clients (net use Z: \\server\share\directory\directory) if you wish to get around this.
3. If "lsmod | grep dm" doesn't report dm_snapshot, add "dm_snapshot" to /etc/modules.
4. If you're on Debian or Ubuntu, check /etc/udev/udev.rules or /etc/udev/rules.d/20-names.rules for a line such as:
KERNEL=="dm-[0-9]*", NAME="dm/%n"
udev doesn't like the creation of devices without it having a say, so change it to
KERNEL=="dm-[0-9]*", OPTIONS+="ignore_device"
Source: udev: LVM snapshots don't work
It would also appear that with XFS, you should ignore any websites that tell you to use xfs_freeze, as this will hang lvcreate.
5. Configure Samba.
I have used something a little like this:
data?
comment = Snapshotted storage
path = /array/storage
read only = no
browseable = yes
force create mode = 0664
force directory mode = 0775
force group = "MYDOMAIN+Domain Users"
writeable = yes
vfs objects = shadow_copy
The important part is, of course, the shadow_copy VFS module.
You end up with an /array/storage directory that looks like this:
drwxr-xr-x 8 root MYDOMAIN+domain users 4096 2006-05-02 12:14 . drwxr-xr-x 3 root root 4096 2006-04-27 11:28 .. drwxr-xr-x 8 root MYDOMAIN+domain users 4096 2006-05-02 07:00 @GMT-2006.05.02-07.00.00 drwxr-xr-x 9 root MYDOMAIN+domain users 4096 2006-05-02 12:00 @GMT-2006.05.02-12.00.00 drwxr-xr-x 9 root MYDOMAIN+domain users 4096 2006-05-03 07:00 @GMT-2006.05.03-07.00.00 drwxr-xr-x 7 root MYDOMAIN+domain users 148 2006-05-03 12:00 @GMT-2006.05.03-12.00.00 drwxrwxr-x 2 root MYDOMAIN+domain users 31 2006-04-27 14:56 public
Samba presents you all of this, @GMT-date dirs and all. Seems you have to have this - you can't share /array/storage/public and have the shadow copies work (see point 2, above).
5. Create some scripts to do the work for you.
OK, here's the fun part.
I have created a rotation I call 'halfdaily', matching Windows 2003 by taking snapshots at 7am and 12pm; "before work" and "before lunch".
One page links to SambaShadowCopyHowto:
