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Old 02-16-2011, 07:19 AM   #16
z1p
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The advantage of using snapshots as the means to get a backup is best seen for applications such as databases where you can greatly reduce the time the database is offline for a backup. For filesystems, it is not as clearcut as if you don't quiesce the filesystem during the snapshot, all you are guaranteed is a crash-consistent image of the filesystem.

As far how secure a snapshot is as a backup, it is directly related to the robustness of your storage back end. Maybe it is best to think of a snapshot as short term data protection, with migrating it to long term storage as an option.

forbin, I agree LVM snapshots are not the solution in and of itself for daily/weekly backup or archiving. But, they definitely are a valid means to get there or to provide short term protection against data corruption. Taking a snapshot before performing a database upgrade, so that you can revert the database if anything should happen is one example of using a snapshot for short term protection.
 
Old 02-16-2011, 10:35 AM   #17
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I see your viewpoint, but I just don't think it qualifies as a backup. That's why all the examples you find on the internet of "how to use LVM snapshots to take a backup" have at least two steps. The first step is to take the snapshot. The second step is to take a backup of the snapshot using tar or something else. (And then a frequent third step that people often suggest is to destroy the snapshot.) Using snapshots alone, I think you end up with a false sense of security. When your "original" and your "backup copy" actually point to most of the same disk sectors, you have a fundamental problem. I can understand why snapshots might be sufficient for some people, but they sure don't work for me.
 
Old 02-16-2011, 10:52 AM   #18
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Quote:
Originally Posted by forbin View Post
I see your viewpoint, but I just don't think it qualifies as a backup. That's why all the examples you find on the internet of "how to use LVM snapshots to take a backup" have at least two steps. The first step is to take the snapshot. The second step is to take a backup of the snapshot using tar or something else. (And then a frequent third step that people often suggest is to destroy the snapshot.) Using snapshots alone, I think you end up with a false sense of security. When your "original" and your "backup copy" actually point to most of the same disk sectors, you have a fundamental problem. I can understand why snapshots might be sufficient for some people, but they sure don't work for me.
That's why I take my snapshots, backup to tape and then store all of the tapes in a cardboard box next to a kindling, fireworks and nitro-glycerine factory. Superb.
 
Old 02-16-2011, 11:23 AM   #19
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Chris, you forgot to mention that the box sits between two huge Marantz disco speakers with 5-pound woofer magnets. :-)
 
Old 02-16-2011, 04:08 PM   #20
z1p
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Quote:
Originally Posted by acid_kewpie View Post
That's why I take my snapshots, backup to tape and then store all of the tapes in a cardboard box next to a kindling, fireworks and nitro-glycerine factory. Superb.
Why didn't I think of that?
 
  


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