When you run a MongoDB backup operation, MongoDB requests a snapshot. This snapshot is created on a Logical Volume Management (LVM) system for each logical volume with data or logs for the selected database. On Linux® systems, logical volumes are managed by LVM2.
A software-based LVM2 snapshot is taken as a new logical volume on the same volume group. The snapshot volumes are temporarily mounted on the same machine that runs the MongoDB instance so that they can be transferred to the vSnap repository.
On Linux, the LVM2 volume manager stores the snapshot of a logical volume within the same volume group. There must be enough space available to store the logical volume. The logical volume grows in size as the data changes on the source volume for the lifetime of the snapshot.