Hi,
James Kyle wrote on 15.05.2007 at 16:01:20 [[BackupPC-users] Should I be
looking to expand or not?]:
> Right now according to BackupPC we have:
>
> 20 full backups of total size 698.96GB (prior to pooling and
> compression),
> 44 incr backups of total size 72.03GB (prior to pooling and
> compression).
>
> The actual disk usage is:
> disk Size Used Available
> /dev/disk3 466G 181G 285G
>
>
> As you can see, our actual backed up data is far in excess of total
> disk space available. Should we be looking to expand our available
> space? I'm not sure if we should be worried about overfilling the
> drive before the nightly compression/pooling is done or not.
no, you shouldn't. BackupPC does not first transfer data and then pool
and compress it.
1.) Compression is always done on-the-fly when storing a new file (not yet
in the pool). No intermediate copy of the uncompressed file is made.
2.) Pooling is "mostly" done on-the-fly. If the file is already "available"
in the pool, no intermediate copy is made on disk. If the file is not yet
"available" in the pool, it is created (compressed, see above). This may
happen independently for multiple copies of identical contents during one
backup run or during "simultaneous" backup runs. During the BackupPC_link
phase, these multiple copies are reconciled to hardlinks to one of these
copies (the others are deleted), at the same time making the contents
"available" to pooling. If there are many outstanding BackupPC_link jobs,
that could take a while, meaning multiple copies could be created.
Usually, BackupPC_link should be run shortly after the backup job though,
so that should not be much of a problem.
The actually amazing thing is that that works without intermediate disk
storage, without storing the complete file in memory and without
retransmitting the data in any case. That is rather important for handling
large unchanged files in full backups.
Regards,
Holger
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