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Re: [linux-lvm] Corrupt PV (wrong size)



On Mon, Mar 19, 2012 at 03:57:42PM -0500, Richard Petty wrote:
> Sorry for the long break away from this topic....
> 
> On Mar 7, 2012, at 2:31 PM, Lars Ellenberg wrote:
> 
> > On Mon, Mar 05, 2012 at 12:46:15PM -0600, Richard Petty wrote:
> >> GOAL: Retrieve a KVM virtual machine from an inaccessible LVM volume.
> >> 
> >> DESCRIPTION: In November, I was working on a home server. The system
> >> boots to software mirrored drives but I have a hardware-based RAID5
> >> array on it and I decided to create a logical volume and mount it at
> >> /var/lib/libvirt/images so that all my KVM virtual machine image
> >> files would reside on the hardware RAID.
> >> 
> >> All that worked fine. Later, I decided to expand that
> >> logical volume and that's when I made a mistake which wasn't
> >> discovered until about six weeks later when I accidentally rebooted
> >> the server. (Good problems usually require several mistakes.)
> >> 
> >> Somehow, I accidentally mis-specified the second LMV physical
> >> volume that I added to the volume group. When trying to activate
> >> the LV filesystem, the device mapper now complains:
> >> 
> >> LOG ENTRY
> >> table: 253:3: sdc2 too small for target: start=2048, len=1048584192, dev_size=1048577586
> >> 
> >> As you can see, the length is greater than the device size.
> >> 
> >> I do not know how this could have happened. I assumed that LVM tool
> >> sanity checking would have prevented this from happening.
> >> 
> >> PV0 is okay.
> >> PV1 is defective.
> >> PV2 is okay but too small to receive a PV1's contents, I think.
> >> PV3 was just added, hoping to migrate PV1 contents to it.
> >> 
> >> So I added PV3 and tried to do a move but it seems that using some
> >> of the LMV tools is predicated on the kernel being able to activate
> >> everything, which it refuses to do.
> >> 
> >> Can't migrate the data, can't resize anything. I'm stuck. If course
> >> I've done a lot of Google research over the months but I have yet to
> >> see a problem such as this solved.
> >> 
> >> Got ideas?
> >> 
> >> Again, my goal is to pluck a copy of a 100GB virtual machine off of
> >> the LV. After that, I'll delete the LV.
> >> 
> >> ==========================
> >> 
> >> LMV REPORT FROM /etc/lvm/archive BEFORE THE CORRUPTION
> >> 
> >> vg_raid {
> >> id = "JLeyHJ-saON-6NSF-4Hqc-1rTA-vOWE-CU5aDZ"
> >> seqno = 2
> >> status = ["RESIZEABLE", "READ", "WRITE"]
> >> flags = []
> >> extent_size = 8192 # 4 Megabytes
> >> max_lv = 0
> >> max_pv = 0
> >> metadata_copies = 0
> >> 
> >> physical_volumes {
> >> 
> >> pv0 {
> >> id = "QaF9P6-Q9ch-bFTa-O3z2-3Idi-SdIw-YMLkQI"
> >> device = "/dev/sdc1" # Hint only
> >> 
> >> status = ["ALLOCATABLE"]
> >> flags = []
> >> dev_size = 419430400 # 200 Gigabytes
> >> pe_start = 2048
> > 
> > that's number of sectors into /dev/sdc1 "Hint only"
> > 
> >> pe_count = 51199 # 199.996 Gigabytes
> >> }
> >> }
> >> 
> >> logical_volumes {
> >> 
> >> kvmfs {
> >> id = "Hs636n-PLcl-aivI-VbTe-CAls-Zul8-m2liRY"
> >> status = ["READ", "WRITE", "VISIBLE"]
> >> flags = []
> >> segment_count = 1
> >> 
> >> segment1 {
> >> start_extent = 0
> >> extent_count = 50944 # 199 Gigabytes
> > 
> > And that tells us your kvmfs lv is 
> > linear, not fragmented, and starting at extent 0.
> > Which is, as seen above, 2048 sectors into sdc1.
> > 
> > Try this, then look at /dev/mapper/maybe_kvmfs
> >  echo "0 $[50944 * 8192] linear /dev/sdc1 2048" |
> >  dmsetup create maybe_kvmfs
> 
> This did result in creating an entry at /dev/mapper/maybe_kvmfs.
> 
> 
> > But see below...
> > 
> >> type = "striped"
> >> stripe_count = 1 # linear
> >> 
> >> stripes = [
> >> "pv0", 0
> >> ]
> >> }
> >> }
> >> }
> >> }
> >> 
> >> ==========================
> >> 
> >> LMV REPORT FROM /etc/lvm/archive AS SEEN TODAY
> >> 
> >> vg_raid {
> >> id = "JLeyHJ-saON-6NSF-4Hqc-1rTA-vOWE-CU5aDZ"
> >> seqno = 13
> >> status = ["RESIZEABLE", "READ", "WRITE"]
> >> flags = []
> >> extent_size = 8192 # 4 Megabytes
> >> max_lv = 0
> >> max_pv = 0
> >> metadata_copies = 0
> >> 
> >> physical_volumes {
> >> 
> >> pv0 {
> >> id = "QaF9P6-Q9ch-bFTa-O3z2-3Idi-SdIw-YMLkQI"
> >> device = "/dev/sdc1" # Hint only
> >> 
> >> status = ["ALLOCATABLE"]
> >> flags = []
> >> dev_size = 419430400 # 200 Gigabytes
> >> pe_start = 2048
> >> pe_count = 51199 # 199.996 Gigabytes
> >> }
> >> 
> >> pv1 {
> >> id = "8o0Igh-DKC8-gsof-FuZX-2Irn-qekz-0Y2mM9"
> >> device = "/dev/sdc2" # Hint only
> >> 
> >> status = ["ALLOCATABLE"]
> >> flags = []
> >> dev_size = 2507662218 # 1.16772 Terabytes
> >> pe_start = 2048
> >> pe_count = 306110 # 1.16772 Terabytes
> >> }
> >> 
> >> pv2 {
> >> id = "NuW7Bi-598r-cnLV-E1E8-Srjw-4oM4-77RJkU"
> >> device = "/dev/sdb5" # Hint only
> >> 
> >> status = ["ALLOCATABLE"]
> >> flags = []
> >> dev_size = 859573827 # 409.877 Gigabytes
> >> pe_start = 2048
> >> pe_count = 104928 # 409.875 Gigabytes
> >> }
> >> 
> >> pv3 {
> >> id = "eL40Za-g3aS-92Uc-E0fT-mHrP-5rO6-HT7pKK"
> >> device = "/dev/sdc3" # Hint only
> >> 
> >> status = ["ALLOCATABLE"]
> >> flags = []
> >> dev_size = 1459084632 # 695.746 Gigabytes
> >> pe_start = 2048
> >> pe_count = 178110 # 695.742 Gigabytes
> >> }
> >> }
> >> 
> >> logical_volumes {
> >> 
> >> kvmfs {
> >> id = "Hs636n-PLcl-aivI-VbTe-CAls-Zul8-m2liRY"
> >> status = ["READ", "WRITE", "VISIBLE"]
> >> flags = []
> >> segment_count = 2
> > 
> > Oops, why does it have two segments now?
> > That must have been your resize attempt.
> > 
> >> segment1 {
> >> start_extent = 0
> >> extent_count = 51199 # 199.996 Gigabytes
> >> 
> >> type = "striped"
> >> stripe_count = 1 # linear
> >> 
> >> stripes = [
> >> "pv0", 0
> >> ]
> >> }
> >> segment2 {
> >> start_extent = 51199
> >> extent_count = 128001 # 500.004 Gigabytes
> >> 
> >> type = "striped"
> >> stripe_count = 1 # linear
> >> 
> >> stripes = [
> >> "pv1", 0
> > 
> > Fortunately simple again: two segments,
> > both starting at extent 0 of their respective pv.
> > that gives us:
> > 
> > echo "0 $[51199 * 8192] linear /dev/sdc1 2048
> > $[51199 * 8192] $[128001 * 8192] linear /dev/sdc2 2048" |
> >  dmsetup create maybe_kvmfs
> > 
> > (now do some read-only sanity checks...)
> 
> I tried this command, decrementing sdc2 from 128001 to 127999:
> 
> [root zeus /dev/mapper]  echo "0 $[51199 * 8192] linear /dev/sdc1 2048 $[51199 * 8192] $[127999 * 8192] linear /dev/sdc2 2048" | dmsetup create kvmfs
> device-mapper: create ioctl failed: Device or resource busy
> Command failed

Well: you need to find out what to use as /dev/sdXY there, first,
you need to match your disks/partitions to the pvs.

> > Of course you need to adjust sdc1 and sdc2 to
> > whatever is "right".
> > 
> > According to the meta data dump above,
> > "sdc1" is supposed to be your old 200 GB PV,
> > and "sdc2" the 1.6 TB partition.
> > 
> > The other PVs are "sdb5" (410 GB),
> > and a "sdc3" of 695 GB...

If "matching by size" did not work for you,
maybe "pvs -o +pv_uuid" gives sufficient clues
to be able to match them with the lvm meta data dump
above, and construct a working dmsetup line.

> > If 128001 is too large, reduce until it fits.
> > If you broke the partition table,
> > and the partition offsets are now wrong,
> > you have to experiment a lot,
> > and hope for the best.
> > 
> > That will truncate the "kvmfs",
> > but should not cause too much loss.
> > 
> > If you figured out the correct PVs and offsets,
> > you should be able to recover it all.
> 
> I understand that the strategy is to reduce the declared size of PV1
> so that LVM can enable the PV and I can mount the kvmfs LV. I'm not
> expert at LVM, and while I can get some things done with it when there
> are no problems, I'm out of my league when problems occur. 

-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.


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