[mythtv-users] MythTV updates, back out plan, lvm snapshots

[Brian J. Murrell]

On 12-02-26 08:05 AM, Brent Bolin wrote:
> Hello All,

Hi,
 
> I've know about lvm snapshots for a while but haven't used it.

Welcome to 1990.  :-)

> Assuming core OS is all in a single lv.

Not a requirement.  I have my /usr and /var in separate LVs from / and
just snapshot all of them.  i.e.:

$ sudo lvs
  LV                   VG          Attr   LSize   Origin      Snap%  Move Log Copy%  Convert
,,,  ubuntu_root          rootvol_tmp owi-ao 500.00m                                           
  ubuntu_root-20111213 rootvol_tmp swi-a- 500.00m ubuntu_root  49.09                        
  ubuntu_root-20120209 rootvol_tmp swi-a- 500.00m ubuntu_root  43.17                        
  ubuntu_root-20120214 rootvol_tmp swi-a- 500.00m ubuntu_root  36.15                        
  ubuntu_root-20120220 rootvol_tmp swi-a- 500.00m ubuntu_root  15.43                        
  ubuntu_usr           rootvol_tmp owi-ao   2.49g                                           
  ubuntu_usr-20111213  rootvol_tmp swi-a-   2.49g ubuntu_usr   34.00                        
  ubuntu_usr-20120209  rootvol_tmp swi-a-   2.49g ubuntu_usr   29.71                        
  ubuntu_usr-20120214  rootvol_tmp swi-a-   2.49g ubuntu_usr   25.40                        
  ubuntu_usr-20120220  rootvol_tmp swi-a-   2.49g ubuntu_usr   14.20                        
  ubuntu_var           rootvol_tmp owi-ao   1.99g                                           
  ubuntu_var-20111213  rootvol_tmp swi-a-   1.99g ubuntu_var   60.55                        
  ubuntu_var-20120209  rootvol_tmp swi-a-   1.99g ubuntu_var   47.15                        
  ubuntu_var-20120214  rootvol_tmp swi-a-   2.49g ubuntu_var   30.73                        
  ubuntu_var-20120220  rootvol_tmp swi-a-   2.49g ubuntu_var   22.28 

[ Please nobody lecture me on the performance impacts of the above
number of snapshots.  I fully understand, and yes, probably do need
to do some snapshot pruning ].

> lvcreate -L8G -s -n rootsnapshot /dev/vol00/root ( in my case )

Yup, repeat for as many mount points as you normally have per above.
 
> And to back out if needed -
> 
> lvconvert --merge /dev/vol00/rootsnapshot ; init 6

It's even easier than that.  Simply boot the snapshot (assuming you
upgraded the origin).  To be more clear, add a new grub entry and
change the root= on the kernel command line in the new entry to
point to your snapshot.  If you do as I do and have a separate /usr
and /var, you of course need to make sure you update /etc/fstab on
the snapshot to boot the snapshotted version of those.

> Granted I've had a back end running for 4 years now.  Never really had
> a problem doing updates other then when changing MythtV releases
> (tweaking etc...).

Well, I run master (for the moment, will switch to 0.25-fixes when 0.25
is released) so I like having the backout plan.

> Don't know how much simpler it can get; to get back to go.

Well, per above, it is even simpler if you simply boot the snapshot.
I've never used the lvconvert --merge facility.  Does it have a time
penalty while it merges the snapshot back up into the origin?

I'd just as soon keep my forks open though so that I can do a port-
mortem should I need to.

Cheers,
b.



-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 262 bytes
Desc: OpenPGP digital signature
Url : http://www.mythtv.org/pipermail/mythtv-users/attachments/20120226/689f8149/attachment.bin