2017-09-22 17:24 GMT+02:00 Gandalf Corvotempesta
<gandalf.corvotempe...@gmail.com>:
2017-09-22 17:20 GMT+02:00 Les Mikesell <lesmikes...@gmail.com>:
How does your overall CPU and RAM use look while this is happening?
Remember, your situation is unusual in that you are competing with the
ZFS compression activity.
CPU almost idle, RAM used at 70%, due to ZFS ARC cache (50% of ram)
No swap.
On 23/9/17 02:50, Gandalf Corvotempesta wrote:
Just removed "--checksum" from the BackupPC arguments.
Now is........... FAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAST
What i've backupped in about 40hours, now took 60 minutes.
YES: 40 hours => 60 minutes.
Is --checksum really needed ? (checksum is also missing from rsnapshot
arguments, that's why rsnapshot is rocket fast)
I can't be sure for BPC4, but maybe you need more than one full backup
to get the checkum information available to BPC. I think on v3 you
needed two full backups before this would happen.
The other point to consider, is that this shows you *DID* have a
performance issue, but you didn't seem to find it. checksum will
increase the read load and CPU load on at least the client (and possibly
BPC server depending on where it gets the checksum info from). So you
should have seen that you were being limited by disk IO or CPU on either
BPC server, or the client. I'm not sure of the memory requirement for
the checksum option, but this too might have been an issue, especially
if BPC tried to uncompress the file into memory. Also, all of this would
trash your disk read cache on both systems, further increasing demands
on the disks.
Whether you need to use --checksum or not, will depend on if you are
happy to potentially skip backing up some files without knowing about it
until you need to do a restore. Of course, this is a little contrived,
as it still requires:
a) size doesn't change
b) timestamp doesn't change
c) content *does* change
That is not a normal process, but it is the corner case that always ends
up being the most important file ;)
Regards,
Adam
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