On 29/10/13 15:14, Sharuzzaman Ahmat Raslan wrote:
Hi Les,


Thanks.|
|


On Tue, Oct 29, 2013 at 11:33 AM, Les Mikesell <lesmikes...@gmail.com <mailto:lesmikes...@gmail.com>> wrote:

    On Mon, Oct 28, 2013 at 10:08 PM, Sharuzzaman Ahmat Raslan
    <sharuzza...@gmail.com <mailto:sharuzza...@gmail.com>> wrote:
    > Hi,
    >
    > I have implemented BackupPC for my customer.
    >
    > Initially, the backup transport is SMB, but recently, I noticed
    a lot of
    > machine backup (full and incremental) is not able to complete in
    8 hours,
    > due to large number of file, and big file size.
    >
    > Last week, I installed DeltaCopy (rsycnd server for Windows) on
    one machine,
    > and change the backup transport to rysncd. The backup runs well.
    >
    > But today, I noticed, when BackupPC is running a full backup on
    the machine
    > that have rsyncd, it still takes 8 hours to do full backup.
    >
    > Which is I considered weird, because rsync suppose to compare
    that full
    > backup, with the previous full backup (or previous full +
    incremental), so
    > that only modified file is transferred.
    >
    > That is my expectation when I plan to use rsyncd.
    >
    > Any explanation why BackupPC is not running in this way? Any
    configuration
    > that I can changed to make it work like what I expect?
    >

    Rsync will only transfer the changed data, but in full runs the
    contents of the files are read at both ends and compared with block
    checksums, so it takes some time.  Incrementals runs will quickly skip
    files where the file timestamps and lengths are identical. See the
    section on 'Rsync checksum caching' in
    http://backuppc.sourceforge.net/faq/BackupPC.html regarding a way to
    avoid having to read/uncompress on the server side after 2 fulls have
    completed, but the data is always read on the target side.

In essence, if I enable
|--checksum-seed=32761

|
then the rsync full backup will be faster?

Yes, the third full backup after you enable that option will be faster *IF* the slow speed is due to the backup server needing to decompress the file and check the content.

In the case that your backup client has really slow disk, then there is nothing you can do, except maybe modify backuppc for full backups to not send the ignore-times option to rsync (ie, every backup is an incremental). Or, of course, upgrade the client to improve performance.

Regards,
Adam



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Adam Goryachev Website Managers www.websitemanagers.com.au
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