Differences between version 12 and predecessor to the previous major change of SambaShadowCopyHowto.
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| Newer page: | version 12 | Last edited on Friday, July 7, 2006 11:50:21 am | by AristotlePagaltzis | Revert |
| Older page: | version 1 | Last edited on Thursday, April 27, 2006 12:10:26 pm | by CraigBox | Revert |
@@ -17,10 +17,134 @@
This document is written using Ubuntu Dapper, but you should be able to use the information on any distribution with new enough components.
* [Samba] 3.0.3 or higher
* A kernel that supports [LVM] and [XFS]
+* An [LVM] volume. Create one, if you haven't already.
-[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. To
be sure
of the integrity
of your snapshot, you need
to do this. It seems like
it's possible
to do this on [Ext3]
file systems
, but without
a similar method
for freezing
, you could lose data
.
+[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|http://oss.sgi.com/bugzilla/show_bug.cgi?id=400] right now. Many filesystems in the kernel support [waiting until the filesystem is consistent before taking a snapshot|http://www.tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html] - you might wish to research this in more detail, but for this HOWTO we will use XFS.
+
+!Steps
+
+1. Join a Windows domain, if you need to. I followed [this howto|http://www.ubuntuforums.org/showthread.php?t=91510], which should
be rolled into our wiki, which is a huge mess
of conflicting information about joining Windows domains that really needs some [Aristotle|AristotlePagaltzis] 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:
+
+<verbatim>
+KERNEL=="dm-[-9]*", NAME="dm/%n"
+</verbatim>
+
+udev doesn't like the creation of devices without it having a say, so change it to
+
+<verbatim>
+KERNEL=="dm-[-9]*", OPTIONS+="ignore_device"
+</verbatim>
+
+Source: [udev: LVM snapshots don't work|http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=343671#msg20]
+
+It would also appear that with XFS, you should ignore any websites that tell you to use xfs_freeze, as [this will hang lvcreate|http://oss.sgi.com/bugzilla/show_bug.cgi?id=400].
+
+5. Configure Samba.
+
+I have used something a little like this:
+
+<verbatim>
+[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
+</verbatim>
+
+The important part is, of course, the shadow_copy VFS module.
+
+You end up with an /array/storage directory that looks like this:
+<verbatim>
+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
+</verbatim>
+
+Samba presents you with just the public directory.
+
+5. Create some scripts
to do the work for you.
+
+!Scripts
+
+OK, here's the fun part.
+
+Because of the way LVM snapshots are created, you assign the amount of space for the changes you think will be made to it. If you assume you will have 1GB of changes every day and will keep snapshots for five days, you could make all your snapshots just over 5GB (including overhead).
+
+I'm being a bit smarter. I'm creating the snapshot at 1GB, and then I'm growing it to 2GB on the second day, 3GB on the third day, etc.
+
+For
this example, I have created a rotation I call 'halfdaily', matching Windows 2003 by taking snapshots at 7am and 12pm; "before work" and "before lunch".
+
+; /etc/snapshots/halfdailytab : The table of snapshot date/times. Scripts will mount and umount these at boot/shutdown, and rotate them as appropriate.
+
+; /usr/local/sbin/create-snapshot : Creates and mounts a snapshot. Parameters is the snapshot name, which is the time of its taking (in ''date +%Y.%m.%d-%H.%M.%S'' format), and an optional snapshot size (in LVM format, ie 20M, 5G).
+
+; /usr/local/sbin/create-snapshot-now: Calculate the time now and create/mount a snapshot with that time, and default snapshot size defined in <tt>create-snapshot</tt>
+
+; /usr/local/sbin/remove-snapshot : Removes, unmounts, and removes the mount point for a snapshot. Parameter is the snapshot name.
+
+; /usr/local/sbin/grow-snapshot : Wrapper for lvextend; grows the snapshot in $1 by the size specied in $2, or by the default growth size defined in the script.
+
+; /usr/local/sbin/mount-all-snapshots : Mounts LVM snapshots into their directories. Intended for use at boot time. Call it with a number of snapshot table files, ie <tt>mount-all-snapshots /etc/snapshots/halfdailytab</tt>; if you have another rotation, you can specify more than one table.
+
+; /usr/local/sbin/umount-all-snapshots : As the name suggests, unmounts the snapshots listed in the table specified on the command line; intended for use at system shutdown time.
+
+; /usr/local/sbin/rotate-halfdaily-snapshots : This script brings it all together. Defined in it are a number of snapshots to keep, snapshot growth size, and the table to keep them in.
+
+! How to set it up
+
+Put this in /etc/cron.d/snapshots:
+
+<verbatim>
+# 7am and 12pm every day
+0 7,12 * * * /usr/local/sbin/rotate-halfdaily-snapshots
+</verbatim>
+
+Put mount-all and umount-all in your startup sequence (FIXME: write this bit)
+
+At 7am and 12pm every day, the script will run
. It will see if
it needs
to expire a snapshot (if there are already the maximum number), and do so if required. It will grow all the snapshots by the defined increment, and it will create a new snapshot.
+
+! Extra for experts
+
+If you want, you can have multiple rotations; it would make sense to have half days for the last 2 days and days for the last week; you can
do this by having another table, /etc/snapshots/dailytab, and creating a rotate-daily-snapshots script to match. (Be sure to up the snapshot size).
+
+You might also like to support non-Windows users, by letting them access the snapshots with NFS or SMB. Try symlinking to them, or writing a script to generate Samba shares to suit.
+
+! Conclusion
+
+Congratulations; all going well you should have a Samba share with shadow copies. You can test it by editing a
file, running <tt>create-snapshot-now</tt>, and editing the same file. After changing it, you should see
a "Previous versions" tab appear on the files properties, with the time that you took your snapshot.
+
+! Notes:
+
+* If you don't change the file, you don't see previous versions
for it.
+* You can do previous versions on directories, as well as files.
+* The snapshots will appear to the Linux machine to be complete copies of the filesystem at that point in time; with the proviso that they are read-only
, you can do what you like with them
.
+
+! Author
+
+CraigBox
!Links
* [How to use the Shadow Copy client|http://www.petri.co.il/how_to_use_the_shadow_copy_client.htm]
+* [Some useful information about XFS & snapshots|http://c.mills.ctru.auckland.ac.nz/Samba/XfsAclWinAuth.html]
+
+----
+CategoryHowto
