[linux-lvm] snapshot with bigmem broken

Heinz J . Mauelshagen mauelshagen at sistina.com
Fri May 16 06:08:02 UTC 2003

On Wed, May 14, 2003 at 06:50:46AM -0400, Lauro, John wrote:
> Hello,
> 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.

> 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.

> PS: As mentioned previously, everything else in LVM seems to be ok
> with larger kernel memory models.  It's mainly just snapshots that
> appear to be broken using the latest LVMs and kernel.


Heinz    -- The LVM Guy --

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


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

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