For the second phase of growth, the online resizer initializes the next group beyond the end of the filesystem. This is easily done because this area is currently unused and unknown to the filesystem itself. The block bitmap for that group is initialized as empty, the superblock and group descriptor backups (if any) are copied from the primary versions, and the inode bitmap and inode table are initialized. Once this has completed successfully the online resizing code briefly locks the superblock to increase the total and free blocks and inodes counts for the filesystem, add a new group to the end of the group descriptor table, and increase the total number of groups in the filesystem by one. Once this is completed the backup superblock and group descriptors are updated in case of corruption of the primary copies. If there is a problem at this stage, the next e2fsck will also update the backups.
The second phase of growth will be repeated until the filesystem has fully grown, or the last group descriptor block is full. If a partial group is being added at the end of the filesystem the blocks are marked as ``in use'' before the group is added. Both first and second phase of growth can be done on any ext3 filesystem with a supported kernel and suitable block device.