[Gluster-users] gluster volume snap shot - basic questions

[Rajesh Joseph]

----- Original Message -----
> From: "Merlin Morgenstern" <merlin.morgenstern at gmail.com>
> To: "Rajesh Joseph" <rjoseph at redhat.com>
> Cc: "gluster-users" <gluster-users at gluster.org>
> Sent: Wednesday, September 2, 2015 11:53:05 AM
> Subject: Re: [Gluster-users] gluster volume snap shot - basic questions
> 
> Thank you Rjesh for your help. I have a thinly provisioned LVM now running
> and can create snapshots on a real device, surviving boot.
> 
> There are 2 other questions rising up now.
> 
> 1. I have a LV with 20G, data is 7G. How is it possible, that I could make
> 3 snapshots, each 7G?
> 
> /dev/mapper/gluster-thinv1                               20G  7.0G   12G
> 38% /bricks/brick1
> 
> /dev/mapper/gluster-7cb4b2c8f8a64ceaba62bc4ca6cd76b2_0   20G  7.0G   12G
> 38% /run/gluster/snaps/7cb4b2c8f8a64ceaba62bc4ca6cd76b2/brick1
> 
> /dev/mapper/gluster-506cb09085b2428e9daca8ac0857c2c9_0   20G  7.0G   12G
> 38% /run/gluster/snaps/506cb09085b2428e9daca8ac0857c2c9/brick1
> 
> /dev/mapper/gluster-fbee900c1cc7407f9527f98206e6566d_0   20G  7.0G   12G
> 38% /run/gluster/snaps/fbee900c1cc7407f9527f98206e6566d/brick1
> 
> /dev/mapper/gluster-d0c254908dca451d8f566be77437c538_0   20G  7.0G   12G
> 38% /run/gluster/snaps/d0c254908dca451d8f566be77437c538/brick1
> 
> 

These snapshots are copy-on-write (COW) therefore they hardly consume any space.
As your main volume change the space consumption of the snapshots also grow.
Check the "lvs" command to see the actual snapshot space consumption.

You can get more detailed information if you search for thinly provisioned LVM and snapshots.


> 2. The name of the snapshot folder is the UUID, My plan is to do a "tar cf"
> on the snapshot and even incremental tars. Therefore I would need the name
> of the folder. How could I pass that name to my bash script in order to
> make a backup of the last snap?
> 

Instead of taking per brick backup you can think of taking backup of the entire snapshot
volume. You can mount the snapshot volume and perform the backup. Use the following command
to mount snapshot volume:
mount -t glusterfs <hostname>:/snaps/<snap-name>/<origin-volname> /<mount_point>

or else if you want to find the name of the snapshot volume (UUID) then run the
following command
gluster snapshot info

> 
> 3. A tar process will take hours on the million files I have. I understand
> this is a snapshot, is there a way to backup a "single" snapshot file
> instead?

Snapshot is maintained in the underlying file-system and I see no way of transferring
it to another system.

> 
> Thank you in advance for sheding some light on this topic
> 
> 2015-09-02 7:59 GMT+02:00 Rajesh Joseph <rjoseph at redhat.com>:
> 
> >
> >
> > ----- Original Message -----
> > > From: "Merlin Morgenstern" <merlin.morgenstern at gmail.com>
> > > To: "gluster-users" <gluster-users at gluster.org>
> > > Sent: Tuesday, September 1, 2015 3:15:43 PM
> > > Subject: [Gluster-users] gluster volume snap shot - basic questions
> > >
> > > Hi everybody,
> > >
> > > I am looking into the snap shot tool, following this tutorial:
> > > http://blog.gluster.org/2014/10/gluster-volume-snapshot-howto/
> > >
> > > While having successfully created the LVM, gluster volume and one
> > snapshot,
> > > there are some questions arrising where I was hoping to find some
> > guidence
> > > here:
> > >
> > > 1. From a working setup as in the example I rebooted and everything was
> > gone.
> > > How can I make this setup persistent, so the gluster share is up and
> > running
> > > after boot.
> > >
> >
> > What do you mean by "everything was gone"? Are you using loop back device
> > as disks?
> > If yes then this is expected. Loop back device mapping is gone after
> > machine restart.
> > You should test with real disk or lvm partition.
> >
> > > 2. I understand that the snaps are under /var/run/gluster/snaps/ and I
> > found
> > > them there. Is it save to simply copy them to another server for backup?
> > My
> > > goal is to create a backup each day and transfer the snaps to an
> > FTP-Server
> > > in order to be able to recover from a broken machine.
> > >
> >
> > Yes, snap of individual bricks are mounted at /var/run/gluster/snaps/. I
> > am assuming
> > that you mean copy of data hosted on the snap brick when you say copy the
> > snap.
> > Are you planning to use some backup software or to run rsync on each brick?
> >
> > > 3. Do I really need LVM to use this feature? Currently my setup works on
> > the
> > > native system. As I understand the tuturial I would need to move that to
> > a
> > > LV, right?
> > >
> >
> > Yes, you need LVM and to be precise thinly provisioned LVM for snapshot to
> > work.
> >
> > > Thank you in advance on any help!
> > >
> > > _______________________________________________
> > > Gluster-users mailing list
> > > Gluster-users at gluster.org
> > > http://www.gluster.org/mailman/listinfo/gluster-users
> >
>