[CentOS-virt] LVM Lockout

Ben M. centos at rivint.com
Thu Oct 15 01:54:56 UTC 2009

 > It may be easier to help if you explain where you're at, where you 
want to be, and what you did to make it worse. :) The dmraid and LVM 
layouts would help, as well as the symptoms you're having.

This is all "Standard CentOS 5.3" install, with X Windows and XFCE4 
loaded afterwards and initiated as command line, not as service. No 
repos other than 'stock'.

I use virt-manager to start of domUs quickly and then edit them to 
polish off.

Small machine, a test case, but will be using pretty much the same for 
the next few builds, only twice the capacity. 4cpu cores, 16gig ram.

- 2X AMD 2212s (2 core by two)
- Tyan Board, ECC Mem 16gig.
- MCP55 nvidia fake raid (I have had good fortune with this chipset).
- Pair of 160g WD Velocipaptors, RAID1 on the BIOS, dmraid on OS.
- DVD plus 160gig pata drive on IDE for odds and ends. 160gig
- ACPI Manufacturer's Table set to Off in BIOS, was troublesome.

Essentially everything is good with exception of a couple of xm dmesg 
WSMR and NMI warnings that are not fatal.

I'm ran decently with above. Fine on domU's with CentOS x86, not sure on 
x64 but don't need it yet. Have Windows 2008 Web Server (x86 version, 
not x64) "running" okay with GPLPV. I say okay because I must be getting 
some sloppy shutdowns due to some Registry Hive and corruption errors. 
It could be that W2K8 is not the stable creature that I found in W2k3. 
It certainly is loaded with an incredible amount of crap that is useless 
and some of which seems to be serving DRM more than system needs. They 
should have called it Vista Server, heh.

Then instability caused by addition of another RAID1 set.

Situation (Where I'm at)
I add in a pair of WD 640g Caviars, not RE types, which I modded a tiny 
bit with WDTyler utility to make them more "raid ready." It's a minor 
trick, but gives you a little more assurance.

They show up in /dev as sd(x)s, but not in /dev/mapper with the nvidia_ 
handle. I type dmraid -ay and there they are, but not auto-magically 
like the first pair do at boot. I don't see a conf file to make this happen

Mistake 1:
Never mount to the "primary" device in mapper, only the ones that end 
with "p1" "p2" etc.

Mistake 2:
Never pvextend a disk into the same vggroup as your / (root). I wanted 
this so I could migrate the extents off of the test domUs that were 
good. That would have been the easy, and slick way.

Probably Mistake 3:
Don't pvextend hard devices at all. Keep VolumeGroups dedicated 
PhysicalVolumes that don't cross over. My initial raidset was 'vg00' and 
the added on pata drive 'vg01' and I was fine with that.

The loss of a LogicalVolume that is on a dropped device is rather 
inelegant. I have not found out what happens if all is contained by a 
dedicated Volume Group (VG) to a dedicated device (PV), but if a 
LogicalVolume (LV) is on another device (PV) than the rest of the LVs 
within that VG then Xen, dom0 and all the domUs are non-booting and 
inaccessible via IP protocols.

fstab entry for a /dev/mapper/raid_device(PartNo)/LVname kills the boot 
if the LV isn't there, whether by hardware drop, or non-initialization 
by dmraid.

All seems fine on one dmraid device box. It is two Raid1s where I am 
hitting a wall. I'm going to try, right now, one more time, with the 
additional raid set, on its own PV/VG setup (e.g. vg02).

Where I was:
Stable with 1 Raid1 set, running out of space.

Where I am:
Unstable after attempting to add additional Raid1 set.

Where I want to be:
2 Raid1 sets
1 "miscellaneous" pata
  and stable.

I am going to try one more time to add the additional RAID1 set with own 
PV and VG and figure out how to move existing domUs to it after I bring 
it to office (150 miles away). I hope I don't have to run back and forth 
to go on the console.

Christopher G. Stach II wrote:
> ----- "Ben M." <centos at rivint.com> wrote:
>>> The metadata should get everything loaded for you out of the
>> initrd,
>>  > as long as it has all of the necessary RAID level drivers in it.
>> I wish. This has been agonizing and it looks like I am going to be 
>> installing a kludge. I'm going to have to accelerate the build of the
>> next ones. I don't have a warm and fuzzy on this machine anymore.
> It may be easier to help if you explain where you're at, where you want to be, and what you did to make it worse. :) The dmraid and LVM layouts would help, as well as the symptoms you're having.

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