still several techniques and some free and proprietary software for recovery of deleted or lost files using file system journal analysis; however, they do not guarantee any specific file recovery. Compression e3compr is an unofficial patch for ext3 that does transparent compression. It is a direct port of e2compr and still needs further development. It compiles and boots well with upstream kernels, but journaling is not implemented yet. Lack of snapshots support Unlike a number of modern file systems, ext3 does not have native support for snapshots, the ability to quickly capture the state of the filesystem at arbitrary times. Instead, it relies on less-space-efficient, volume-level snapshots provided by the Linux LVM. The Next3 file system is a modified version of ext3 which offers snapshots support, yet retains compatibility with the ext3 on-disk format. No checksumming in journal ext3 does not do checksumming when writing to the journal. On a storage device with extra cache, if barrier=1 is not enabled as a mount option (in /etc/fstab), and if the hardware is doing out-of-order write caching, one runs the risk of severe filesystem corruption during a crash. This is because storage devices with write caches report to the system that the data has been completely written, even if it was written to the (volatile) cache. If hard disk writes are done out-of-order (due to modern hard disks caching writes in order to amortize write speeds), it is likely that one will write a commit block of a transaction before the other relevant blocks are written. If a power failure or unrecoverable crash should occur before the other blocks get written, the system will have to be rebooted. Upon reboot, the file system will replay the log as normal, and replay the "winners" (transactions with a commit block, including the invalid transaction above, which happened to be tagged with a valid commit block). The unfinished disk write above will thus proceed, but using corrupt journal data. The file system will thus mistakenly overwrite normal data with corrupt data while replaying the journal. If checksums had been used, where the blocks of the "fake winner" transaction were tagged with a mutual checksum, the file system could have known better and not replayed the corrupt data onto the disk. Journal checksumming has been added to ext4. Filesystems going through the device mapper interface (including software RAID and LVM implementations) may not support barriers, and