How to Recover XenServer Physical Volume Structure after Accidental Deletion

This article describes how to recreate a Physical Volume (PV) and restore Logical Volume Manager (LVM) structure in a situation where Shared or Local storage metadata has been damaged or overwritten.

Warning! Perform the instructions at your own risk. It is recommended to raise a case with Citrix Technical Support to confirm the cause of the issue and then perform necessary steps. Do not attempt commands in this article unless you are confident in understanding of the issue and suggested steps.

If a PV information has been accidentally deleted or tempered with, LVM commands such as “lvscan”, “vgscan”, and “pvscan” return incorrect or empty output.

Note: The commands lvscan, vgscan, and pvscan also return empty output if storage is disconnected or XenServer has problems with communicating to the storage device. Ensure that storage is attached and can be accessed from XenServer, by testing reading with hdparm –t /dev/sd<x> or hdparm –t /dev/mapper/<scsi id> for multipathed SRs, before proceeding with the following instructions. Correct output returns the PV associated with block device and corresponding Volume Groups.

For instance, correct output of pvscan command for shared SR (iSCSI or HBA) with multipath enabled would be in the following format.

PV /dev/mapper/<scsi id> VG VG_XenStorage-<SR uuid> lvm2 [<size total/size free>]

Note how the block device appears under /dev/mapper. If multipath is not enabled, PV value would point to a single block device /dev/sd<x>, like in case of the local storage. For example:

PV /dev/sda3 VG XSLocalEXT-fdf91589-39f4-4104-9856-3cb6c606255 lvm2 [457.75 GB / 0 free]

If only /dev/sd<x> device is displayed, you can confirm scsi id of that device by inspecting output of command.

ls –alh /dev/disk/by-id/


For example, if there is an iSCSI device with scsi id of “23237636464633731” and uuid “e79f14b6-055e-a166-42ce-bf535db5f285”, as seen in general tab of the SR in XenCenter, then the pvscan output for this SR is as follows.

PV /dev/mapper/23237636464633731 VG VG_XenStorage-e79f14b6-055e-a166-42ce-bf535db5f285 lvm2 [1.22 TB / 116.00 GB free]

However, when LVM has been tempered with, pvscan command may provide no output for that SR, or another Volume Group (VG_XenStorage-<different uuid>) name will be assigned to the PV on the expected scsi device.

Background

This problem can occur in following or similar cases:
  1. Storage has been accidentally mapped to another XenServer pool and/or PV and VG metadata has been removed or overwritten with new PV and VG information.
  2. LVM metadata has been removed with incorrect pv/vg commands executed on the host.

  3. Storage failure that caused corruption on the LUN affecting LVM metadata.

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The Docker build files and Vagrant boxes files for 18c XE have also been updated to take advantage of this change and no longer require the user to download the software first either!

This change has been requested by the community. Oracle continues its commitment to the community and will base future releases of XE, Windows and Linux alike, under the Free Use Terms and Conditions license as well.

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The vulnerability is due to an incorrect configuration of the authentication settings on the JBoss EAP. An attacker could exploit this vulnerability by authenticating with a specific low-privilege account. A successful exploit could allow the attacker to gain unauthorized access to the JBoss EAP, which should be limited to internal system accounts.

Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200102-dcnm-unauth-access

Security Impact Rating: Medium

CVE: CVE-2019-15999

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