Re: compression in dump(8)

[Lyndon Nerenberg]

On 2016-05-02 2:29 PM, Robert Elz wrote:

I do

gzip -d < /path/do/mydump | restore -if -

all the time, it works just fine.


And that's because dump/restore were built to work with tapes, where 
backspace/rewind is evil.  This is why the multiple passes during 
dump – it writes a table of contents at the start of the dump set so it 
knows where to find everything on the tape(s). (More or less.)

Re: compression in dump(8)

[Swift Griggs]

On Mon, 2 May 2016, Christos Zoulas wrote:
> It does; the dump format puts the directory info first so that it can 
> restore the stuff you selected in a single pass (it does not need to 
> seek backwards).

Gotcha. Sorry for piping up about something that already works then! I'll 
be sure to try it next time I need to. 

> Of course if you select some, restore, try to select some more, 
> restore... It will not work since it will need to seek backwards then. 

Understood. That makes good sense. 

> Remember all this stuff was designed with tapes in mind, not random 
> access devices.

Roger that. 


-Swift

Re: compression in dump(8)

[Christos Zoulas]

In article ,
Swift Griggs   wrote:
>On Mon, 2 May 2016, Christos Zoulas wrote:
>> Doesn't that work? zcat dump.gz | restore -f -
>
>Yes it does. What I don't believe will work is this (interactive restores 
>when I only want to restore a few files):
>
>restore -i -f /path/to/mydump

It does; the dump format puts the directory info first so that it
can restore the stuff you selected in a single pass (it does not
need to seek backwards). Of course if you select some, restore,
try to select some more, restore... It will not work since it will
need to seek backwards then. Remember all this stuff was designed
with tapes in mind, not random access devices.

christos

Re: compression in dump(8)

[Swift Griggs]

On Mon, 2 May 2016, Christos Zoulas wrote:
> Doesn't that work? zcat dump.gz | restore -f -

Yes it does. What I don't believe will work is this (interactive restores 
when I only want to restore a few files):

restore -i -f /path/to/mydump

-Swift

compression in dump(8)

[Swift Griggs]

I notice that the dump command in NetBSD doesn't feature the use of any 
internal compression. If one compresses the dump file, then you can't use 
it as the basis for a restore. 

Is that because the compression functions aren't in libc (ie.. they are 
off in libz or liblzma) ? Perhaps it's just a matter of someone doing the 
work ? It'd be a big help for admins who want to be able to use a modern 
compression algorithm without having to uncompress the dump to use it. I 
for one, would use it on all my systems. 

-Swift