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Date: Sun, 31 May 2009 23:39:44 -0700
From: Eddie Atherton <stunnel@attglobal.net>
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Subject: [linux-lvm] highmem64G Breaks My LVM
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To: linux-lvm@redhat.com

I originally posted this on the LinuxQuestions forum:  
http://www.linuxquestions.org/questions/slackware-14/highmem64g-kills-lvm-728418/

I have a fairly vanilla Slack 12.2 system.  I recently upped my memory 
to 8GB, and so recompiled the kernel, making a single change.  HIGNMEM4G 
was changed to HIGHMEM64G.  On re-booting, I could see the extra memory, 
but, unfortunately, I lost all my LVM volumes.

After a few checks, I found that vgscan was failing:

root@The-Tardis:~# vgscan --mknodes --verbose
    Wiping cache of LVM-capable devices
    Wiping internal VG cache
  Reading all physical volumes.  This may take a while...
    Finding all volume groups
  /dev/sda1: Checksum error
    Finding all logical volumes

If I reboot back to the HIGHMEM4G kernel, then all works fine again:

root@The-Tardis:~# vgscan --mknodes --verbose
    Wiping cache of LVM-capable devices
    Wiping internal VG cache
  Reading all physical volumes.  This may take a while...
    Finding all volume groups
    Finding volume group "raid_vg"
  Found volume group "raid_vg" using metadata type lvm2
    Finding all logical volumes

All the LVM volumes reside on an LSI megaRAID card, detected as 
/dev/sda, which is dedicated to a single PVM.

Any ideas why changing the HIGHMEM kernel option would break LVM.

Cheers,
Eddie