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ext4 (1).docx - Basharat Anis Extra Credit Paper: EXT4 File...

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Basharat AnisExtra Credit Paper: EXT4 File SystemAbstract: Ext4 file system is the ext3 file system successor. It is supported on today’s most popular Linux distributions (RedHat, Ubuntu, Fedora). In contrast to the 32-bit ext3 file system, that has only some features added to its predecessor ext2 and maintains a data structure as in the ext2 file system, the ext4 file system has integrated more substantial changes compared to ext3. Ext4 has improved data structure and enhanced features, which brought more reliability and efficiency. It is a 64-bit, allowing the file size of up to 16 TB. Great efforts that have been put into the process of ext4 development resulted in new features and techniques: extents, journaling check summing, simultaneous allocation of multiple units, delayed allocation, faster fsck (file system check), and online defragmentation of small and large size directories. This way formed folders can have up to 64,000 files.The ext4 filesystem can support volumes with sizes up to 1 exbibyte (EiB)and single files with sizes up to 16 tebibytes (TiB)with the standard 4 KiBblock size.[12]The maximum file, directory, and filesystem size limits grow at least proportionately with the filesystem block size up to the maximum 64 KiB block size available on ARMand PowerPC/Power ISACPUs.ext4 is backward-compatiblewith ext3and ext2, making it possible to mountext3 and ext2 as ext4. This will slightly improve performance, because certain new features of the ext4 implementation can also be used with ext3 and ext2, such as the new block allocation algorithm, without affecting the on-disk format.ext4 can pre-allocate on-disk space for a file. To do this on most file systems, zeroes would be written to the file when created. In ext4 (and some other files systems such as XFS) fallocate(), a new system call in the Linux kernel, can be used. The allocated space would be guaranteed and likely contiguous. This situation has applications for media streaming and databases.ext4 uses checksumsin the journal to improve reliability, since the journal is one of the mostused files of the disk. This feature has a side benefit: it can safely avoid a disk I/O wait duringjournaling, improving performance slightly. Journal checksumming was inspired by a research article from the University of Wisconsin, titled IRON File Systems(specifically, section 6, called "transaction checksums"), with modifications within the implementation of compound transactions performed by the IRON file systemEXT4 File System: The EXT4 filesystemprimarily improves performance, reliability, and capacity. To improve reliability, metadata and journal checksums were added. To meet various mission-critical requirements, the filesystem timestamps were improved with the
addition of intervals down to nanoseconds. The addition of two high-order bits in the timestamp field defers the Year 2038 problemuntil 2446—for EXT4 filesystems, at least.

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