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Re: [BackupPC-users] High Repeated Data Transfer Volumes During Incremental Backup
2011-04-01 11:02:36
On 2011-03-31 15:47 John Rouillard wrote:
> The only way the March 30'th backup wouldn't
have transferred the
> files was if the march 29th backup was a level 1 incremental and the
> march 30'th was a level 2 incremental. In that case the march 30'th
> incrementals reference tree would have been from the march 29 backup
> which already had the files in the new (moved) location and it would
> have been able to determine that the files were identical.
> Transfer decisions are based on the file names
under the pc
> directory. If the file doesn't exist in the comparison tree (which
is
> taken from the previous higher level backup for incrementals IIRC)
it
> is transferred. Different names/path result in the file being
> transferred again.
> Pooling decisions are based on the checksums of the files that were
> transferred. Newly transferred files are checksummed and compared
to
> files in the pool. So after the transfer occurred pooling should have
> happened and those newly transferred files would have been hardlinked
> into the pooled file.
John, I am having trouble reconciling
what I see with your description. As far as I know, I do only one
level of incremental backups with a full backup once a week. I see
where backuppc is checking date stamps of the incrementals against the
last full backup. However, the backup data transfer volumes suggest
that the entire file is only transferred once. My typical daily Internet
bandwidth is around 300-500MB. The two 350MB files were uploaded
March 20th. The incremental backup on the next day bumped my Internet
usage to 1,480MB. The next day was also an incremental backup but
my Internet usage was only 480MB.
The incremental backup on March 29th
bumped up my Internet usage to 990MB. Even if backuppc decided it
had to download the entire files because they were in a different path,
I would have expected that the incremental backup on March 30th would have
noticed that the files were already in the pool. However, the Internet
usage on March 30th was over 700MB when I checked early in the morning.
The full backup later that day 'got it right' and only backed up
40MB.
I run a bunch of MediaWiki sites, all
of which used the same code base but each site installed the code in its
own directory structure. My recollection is that backuppc only physically
transferred one set of code files. The additional sites did not result
in the same files being transferred again, even though they were in different
paths.
My suspicion is that backuppc gets confused
if files were backed up/excluded/unexcluded or backed up/moved. I
will need to test out various scenarios with tracing enabled, but won't
get a chance for while.
Thanks,
Norbert
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