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Old 03-11-2006, 02:37 AM   #1
sjtushi
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LVM Snapshot question


I don't know what happen when I have made a snapshot of a filesystem. What is in the snapshot LV? When I remove some files from my filesystem which has been taken a snapshot, these files still can be gotten from my snapshot LV. Are these files removed to the snapshot LV?
What are saved in the snapshot logic volume?


Thanks!
 
Old 03-12-2006, 01:26 AM   #2
WhatsHisName
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Whenever a file is modified in a logical volume that has a snapshot running, a copy of the original, unmodified file is retained in the snapshot.

The snapshot allows you to “freeze” the filesystem at an arbitrary point in time while allowing the original logical volume to remain in use.

Although the word “snapshot” seems to infer that it is a full duplicate of the original logical volume, it is not. The snapshot only contains the originals of files that have changed since it was created.

The snapshot is especially useful when backing up a filesystem that is actively being used. When a logical volume snapshot is mounted and its contents copied to tape, to another drive, etc., what you get is an exact duplicate of the entire original logical volume at the moment the snapshot was created.
 
Old 03-12-2006, 02:20 AM   #3
sjtushi
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Thank you for your message!

I have another question : A file is divided into many blocks and storaged in the filesystem.When a file has been changed, is the entire file is moved to the snapshot LV? or only the original blocks which are changed in the filesystem are moved to the snapshot LV?
 
Old 03-12-2006, 09:41 AM   #4
WhatsHisName
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Just the blocks that have changed are copied (or at least that’s what the documentation says).

See: http://www.ibiblio.org/pub/Linux/doc...#snapshotintro
 
  


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