[linux-lvm] snapshot with bigmem broken

[Heinz J . Mauelshagen]

On Fri, May 16, 2003 at 08:38:23AM -0400, Lauro, John wrote:
> > > I did more testing, and it appears that snapshots in LVM will not
> work
> > > with either 4GB or or 64GB support enabled in the kernel under
> 2.4.20.
> > > This includes both LVM 1.0.7 or the latest LVM2.
> > >
> > 
> > That's a known issue. You are faced with a VM flaw.
> > 
> > I presume that it's not LVM snapshots only bacause HIGHMEM is
> > basically broken.
> 
> Can you give more specifics/examples/web links/etc?

No. This is based on our test results.
I reported the highmem problem months ago on linux-kernel.

> Does this mean I
> should avoid LVM completely with HIGHMEM?

No. The problem seems to be limited to snapshots.

> What if any other problems
> should I expect with LVM (and/or other software)?

Any that we and the maintainers of other software are not aware of ;)

> 
> > > Is there anyone using LVM snapshots with 64GB RAM support (or even
> 4GB
> > > RAM support, as snapshots would be good for at least our medium
> size
> > > servers if not our large ones)?  Is so, let me know the kernel
> version
> > > and LVM version you are using so that I can try it.
> > 
> > Probably not, because the system lifelocks on bounce buffers (which
> is
> > the sympton of the principle HIGHMEM bug).
> > Obviously not a lot of HIGHMEM users out there raising priorities to
> fix
> > this.
> 
> Is this easy to reproduce?  If so, how?  Sounds like I am either a
> lucky early adopter of a >4GB Libux system, and/or the problem is rare
> even on HIGHMEM systems?
> 
> Thanks.
> 
> 
> _______________________________________________
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> linux-lvm at sistina.com
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

-- 

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

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Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen at Sistina.com                           +49 2626 141200
                                                       FAX 924446
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