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RE: sparse loop devices and ext3



Thanks - at least it has been explained what it is. 

Sparse loopback file systems are really nice test animals though!

- Peter -

 > -----Original Message-----
 > From: ext3-users-admin redhat com 
 > [mailto:ext3-users-admin redhat com]On
 > Behalf Of Andreas Dilger
 > Sent: Monday, February 12, 2001 11:06 AM
 > To: ext3-users redhat com
 > Subject: Re: sparse loop devices and ext3
 > 
 > 
 > Stephen writes:
 > > On Fri, Feb 09, 2001 at 06:55:15PM -0800, Peter J. 
 > Braam wrote:
 > > > It has a function create_missing_block, that calls 
 > f_write. So it should
 > > > allocate within an ext3 transaction.  So where is 
 > all this corruption
 > > > coming from: probably the fix to 5e you sent in a 
 > few days ago.
 > > 
 > > The 0.0.5e bug might mean that the data flush is not 
 > synchronised to
 > > the metadata flush if you are using ordered data 
 > mode.  However, loop
 > > device writes using bmap are *never* journaled, and 
 > the metadata
 > > updates from the write() allocation will still be journaled.
 > > 
 > > What exactly is the desired behaviour?  For loop writes to be
 > > data-journaled?  That will require changes to the 
 > loop device to
 > > prevent it from ever using bmap().
 > 
 > I think the problem is that if you are loopback 
 > mounting a file, the ext3
 > code itself doesn't consider the loopback file contents 
 > as "metadata" for
 > the underlying file, so it is not journaled, even 
 > though it is metadata
 > in the loopback filesystem.
 > 
 > Peter, I think there are several workarounds for this - 
 > don't make sparse
 > backing files, or mark the backing file as 
 > "data=journal", or don't use
 > loopback files.  I'm not sure what you are working on, 
 > so I can't say
 > what is best in this case.
 > 
 > Cheers, Andreas
 > -- 
 > Andreas Dilger  \ "If a man ate a pound of pasta and a 
 > pound of antipasto,
 >                  \  would they cancel out, leaving him 
 > still hungry?"
 > http://www-mddsp.enel.ucalgary.ca/People/adilger/       
 >         -- Dogbert
 > 
 > 
 > 
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 > 





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