Server is getting hung while taking backups using logical volume manager snapshot

Issue

• Server is getting hung while taking backups using logical volume manager snapshot. Below are the steps used to take backup which lead to hang:
  o The base lvm volume /dev/dbvg/dblv for which the backup was required to be taken, was in use by users and there were large number of IO operations going on it.
  o Created an lvm snapshot /dev/dbvg/dblv from base lvm volume /dev/dbvg/dblv, using following command:

  # lvcreate --snapshot --size 8G --name dbsnap /dev/dbvg/dblv
  

  o Set the following options in /etc/lvm/lvm.conf file so that snapshot will get autoextended, if it gets filled up while taking a backup:

  snapshot_autoextend_threshold = 70
  snapshot_autoextend_percent = 50
  

  o Once the snapshot was created successfully, started Commvault backup application to take backup using above snapshot lv.
  o All the read IO operation on snapshot lvm volume got hung and SysRq was triggered manually to capture vmcore.