Re: [Xen-users] Xen with LVM

[Pierre-Alain RIVIERE <pariviere@xxxxxxxx>]

IDAGroup - R.W.Muller wrote:
> Hi Errol
>
> Errol Neal wrote:
> > Quoting "IDAGroup - R.W.Muller" <robin@xxxxxxxxxxx>:
> >
> > > Hello Errol, I tried that and get a little weird partition table:
> > >
> > > sfdisk -l -uS /dev/vms/centos5_data
> > >
> > > Disk /dev/vms/centos5_data: 0 cylinders, 0 heads, 0 sectors/track
> > > Warning: The partition table looks like it was made
> > >  for C/H/S=*/255/63 (instead of 0/0/0).
> > > For this listing I'll assume that geometry.
> > > Units = sectors of 512 bytes, counting from 0
> > >
> > >   Device Boot    Start       End   #sectors  Id  System
> > > /dev/vms/centos5_data1   *        63   3068414    3068352  83  Linux
> > > /dev/vms/centos5_data2             0         -          0   0  Empty
> > > /dev/vms/centos5_data3             0         -          0   0  Empty
> > > /dev/vms/centos5_data4             0         -          0   0  Empty
> > I wouldn't worry too much about that. sfdisk is probably just 
> > confused. Since the file doesn't have a ioctl, that would be my guess
> Ok I just ignore this partitions :)
> > > Now I just have to find out, how I can get ride of the Empty partitions
> > > and how to use snapshot for backup and I'm getting closer
> > > to a usable result :)
> > lvcreate -L1G -n vmsnap /dev/vms/centos5_data
> >
> > Then mount it as above. Keep in mind that for snapshots, all changes 
> > to the live volume are written to the COW table on the snapshot 
> > volume. Make sure you allocate enough space for this.
> Ok, that means I need at least douple the hardware space then the size 
> of the LV, or I'm wrong with this?
> ....let's say my LV centos5 is 80GB in size, will I need a 160GB 
> harddrive in this blade server in order to get the snapshot and then 
> mount and rsync it to another harddrive? ...or what do you recomment
> for backup purpose?
>
> Thanks,
> Robin
You don't need to allocate the double size of your original LV.  As Erol 
said, you have just to allocate enough space to contains all changes 
made (i.e. writing) on the original partition during the snapshot life.
For example if a snapshot is created à 00:00 am and deleted at 03:00 am, 
and there's no activity on the original LV, you don't need that much 
space (just to contains syslog writing or things like this). But if 
there's extensive usage of your original LV you need to allocate more. 
Writing 600MB (downloading, whatever, ...) of data in your original LV 
requires snapshots of at least 600MB.
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