The ext4 file system in Linux systems is the successor of the ext3 file system. As ext3 was extensively used for quite a long period, the ext4 file system is loaded with lot of new changes to overcome the limitations of ext3 file system. Few important data structures have been added in the ext4 file system to make it provide improved performance, new features, and reliability along with a better design. One such feature is the delayed allocation feature, which does not write any new data as soon as it is entered. Because of this, the processor waits till the time it is really necessary to write the data to the disk as it optimizes the write processes.
However, sometimes the delayed allocation feature results in severe data loss. You should use appropriate methods to resolve the situation. If you are not able to restore the lost data, then you should use a third-party Linux data recovery software to perform ext4 recovery.
Consider a scenario wherein you are using Ubuntu 9.04 with ext4 file system. There is a sudden power outage and the system shuts down abruptly. When the power is restored, you find that the files that you modified just before the shut down are showing ZERO bytes size.
The root cause of this problem is that because of the delayed allocation feature, when a file is written it is noted in the journal. But, it is not written to the disks until a gap of about 45 to 150 seconds. If you modify an existing file or create a new file, then the changes may not reflect after the power loss.
To resolve this absurd situation, you should download the 2.6.30 version of Linux kernel. This should be able to address the issue. However, there are chances that you may still face the same problem even after using the newer version. In such cases, you should use a third-party Linux data recovery software to restore the lost files. Such tools are read-only in nature that do not overwrite the existing data while scanning the hard disk.
Stellar Phoenix Linux Data Recovery is a Linux data recovery software that enables you to recover lost, deleted, or formatted data from inaccessible hard drives. It is able to perform data recovery of Linux systems from various hard drives such as SATA, IDE, EIDE, etc. Apart from FAT12, FAT16, and FAT32 file systems, this Linux recovery tool is capable of performing ext2 recovery, ext3 recovery, and Ext4 file Recovery ext4 data recovery. This tool supports various Linux distributions such as Red Hat, SUSE, Debian, Caldera, Mandrake, Sorcerer, TurboLinux, Slackware, Gentoo, etc. It is compatible with Windows 7, Vista, Server 2003, XP, and 2000.
Source by Kuldeep Kulmii