Dump questions

Dan Nelson dnelson at allantgroup.com
Sun Feb 21 07:50:28 UTC 2010

In the last episode (Feb 21), Aiza said:
> Dan Nelson wrote:
> > In the last episode (Feb 21), Aiza said:
> >> 1. Using the -L flag to create a snapshot of the live running file
> >> system.
> >>
> >> Does this mean that a complete copy of the file system is written to
> >> .snap directory?
> > 
> > No; that would be a "copy".  Snapshots only copy blocks as they are
> > modified on the parent filesystem, so their size is determined by how
> > much data is modified since the snapshot was created.
> So how does this interact with the dump process?
> Dump start reading and writing its dump file and as the live system
> changes the changes are written to the .snap and when dump completes it
> overwrites it dump with the changes from the .snap???
> How does this process work in detail?

Dump reads from the snapshot, which is guaranteed not to change while dump
is running.  When its done, dump deletes the snapshot file.  Changes made
after the dump has started will not be saved.  This is the same as any other
backup system that uses snapshots afaik; none try and catch up changes made
while the backup itself is running.  You could run another incremental dump
right after the previous one, which would back up any changes since the
first one.

	Dan Nelson
	dnelson at allantgroup.com

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