On Mon, Feb 18, 2002 at 04:48:44AM +0100, Esger Abbink wrote:
> Ok, so with one backup (media file?) per tape it really doesnt matter either
> way.
>
A "media file" refers to the data between file marks on the
tape (as one can set with "mt -f tape weof").
xfsdump in tape mode, splits up the dump into media files;
typically each of size 256Mb (50Mb for QIC tapes, or user-definable
with -d).
[On IRIX, the media file size is based on the tape device
sub-type field (which isn't available in Linux),
with 512Mb for DAT, 2GB for Exabyte, 4GB for DLT,...]
--Tim
> ----- Original Message -----
> From: "Timothy Shimmin" <tes@xxxxxxxxxxxxxxxxxxxxxxx>
> To: "Esger Abbink" <e.abbink@xxxxxxxxx>
> Cc: <linux-xfs@xxxxxxxxxxx>
> Sent: Monday, February 18, 2002 4:05 AM
> Subject: Re: xfsdump & compression? (was: Re: xfsdump aborts after assertion
> failure)
>
>
> > my 2 cents...
> >
> > On Mon, Feb 18, 2002 at 02:52:13AM +0100, Esger Abbink wrote:
> > > So, as i understand it there is no "safe" compression aside from
> hardware
> > > compression while using xfsdump.
> > >
> > I think "safe" is a subjective thing here.
> > I think it is more a question of "safer".
> > Option 2 may still be considered viable for some.
> > If one has tape errors then things probably aren't going to be pretty ;-)
> > If one uses the tape strategy (e.g. by "-f /dev/st0" as opposed
> > to stdout), and something happens to the tape such that we
> > get an error on reading on restore - then it allows us to
> > move onto the next media file in the dump. But this is only
> > of some comfort -> the rest of the data in the corrupt media
> > file is gone, we may only have one media file, there may be
> > other errors in other media files.
> >
> >
> > (Hmmm.. and if one was desperate to restore as much as possible,
> > and one had a tape error, then having gzip'ed data would
> > probably make things pretty tricky to recover stuff.)
> >
> > --Tim
> >
> > > as the data volume is quite big, i really need compression.
> recommandations
> > > for backup software anyone?
> > >
> > > ----- Original Message -----
> > > From: <ivanr@xxxxxxx>
> > > To: "Bernhard R. Erdmann" <be@xxxxxxxxxxx>
> > > Cc: "Esger Abbink" <e.abbink@xxxxxxxxx>; <linux-xfs@xxxxxxxxxxx>
> > > Sent: Monday, February 18, 2002 2:22 AM
> > > Subject: Re: xfsdump & compression? (was: Re: xfsdump aborts after
> assertion
> > > failure)
> > >
> > >
> > > > On Sat, 16 Feb 2002, Bernhard R. Erdmann wrote:
> > > >
> > > > > > how do i get xfsdump to compress stuff?
> > > >
> > > > xfsdump does not compress stuff.
> > > >
> > > > > 1. use hardware compression
> > > > > 2. xfsdump -J -F - / | gzip | dd of=$TAPE bs=32k
> > > >
> > > > Option 2 will nullify all of xfsdump's fault tolerance features when
> > > > writing to tape. In other words, if there's a tape error or you hit
> the
> > > > end of tape, xfsdump can't recover.
> > > >
> > > > I understand of course that this might be fine for some, but many
> sites
> > > > don't like to take chances with their backups. Just thought I'd
> mention
> > > > this in case it was an issue.
> > > >
> > > > Ivan
> > > >
> > > > --
> > > > Ivan Rayner
> > > > ivanr@xxxxxxx
> > > >
> > >
> > >
>
>
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