full backup remotely?

[geoffrey mendelson]

On Dec 31, 2009, at 11:58 AM, Michael Ben-Nes wrote:

> To avoid changes on the fly its possible to use snapshot.
>
> I am wondering, what will happen if ill feed dd through gzip. Will  
> it compress the empty spaces ?


At that level there are NO empty spaces. Every block has something in  
it. What you call empty space is just blocks that have not been  
allocated to a file.

If the disk has never been used since the last full format, the blocks  
contain zeros, and will compress to almost nothing. As the disk gets  
used, the blocks continue to contain the same data they did when they  
contained files, unless you erase files as you delete them. I know  
MacOS has such an option if you empty the trash, but the base  
operating system underneath (BSD) does not.

I've never heard of there being a Linux option to do so, but there  
might be.

I still don't understand this fascination with DD. It produces an  
image of the file system, but does anyone really want that? Unless you  
are going to place it back on the same device, or an exact duplicate,  
it's not very good. You can easily end up with an unreadable file  
system, empty space, etc.

The only advantage I can see to doing it is that you don't have as  
much overhead because you are not opening each file. A single read  
error will crash the backup. Better IMHO to use tar or rsync.

Geoff.

-- 
geoffrey mendelson N3OWJ/4X1GM
Jerusalem Israel geoffreymendelson at gmail.com
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge  
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