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  1. With rsync, is it acceptable to modify some files in a file system, while backing up the file system?

    If yes, is it necessary to take a snapshot before backup, and do an incremental backup after finishing modifying the files to keep the backup and the source the same?

  2. Which is better:

    • wait and not change any files during a full backup, or
    • modify some files during a full backup and then do a incremental backup after modifying the files?

    I want to change some files of a large file system while backing it up, because I heard that incremental backup will be much faster than a full backup. Is that correct? So I can wait shorter for backing up?

  3. How do we do snapshot with rsync?
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Some clarification of the question may be required. Rsync will make a copy of the source directory. If you perform an rsync and then alter the destination those changes would be overwritten during the next rsync.

If you're only looking to modify the source I would recommend taking a look at incremental backups with rsync. I use a script based on this method to perform incremental backups of my system. What's nice about this method is that you don't need to reconstruct your files (merging incremental and full) when you restore files.

Since this method utilizes hard links I would not recommend modifying the destination files.

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  • (1) To your first paragraph: I meant modifying some files in the source (not the destination) while backing up the source. Taking a snapshot of the source during it is changing is to get a nonchanging source to backup, although the nonchanging source will be outdated. (2) To your third paragraph: I meant that you have multiple backups created over the time with the first one full backup and the latter ones incremental backups. Since an incremental backup contains hard links to files in the previous backup, why can't we delete the previous backup? – Tim Feb 26 '15 at 18:42
  • I am not sure "snapshot" in your linked article mean the same as "snapshot" in my post? – Tim Feb 26 '15 at 18:48
  • (1) In that case I would take a "full" backup, make your changes, and then create a post-change snapshot. (2) That's one of the beauties of this method. You can delete the previous backups, I didn't mean to imply you couldn't. I was only stating that if you modify files in the destination it would potentially effect multiple "snapshots" since the unchanged files are hardlinks. – SeeJayEmm Feb 26 '15 at 20:50
  • I re-read your question and I think I understand the problem. You have a large file system that will take a long time to backup. You'd like this file system to remain live (r/w access) while the rsync backup is running and still have a backup of the file system in the state it was in when you started? – SeeJayEmm Feb 26 '15 at 21:02
  • for your last comment, yes. By taking a quick snapshot of the source, the backup program can backup the snapshot regardless of what change is being and will bemade to the source. Can rsync work with my onging file changing in the source? – Tim Feb 26 '15 at 21:04

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