File system block

Logical file system — It manages metadata information about a file i. It also maintains via file control blocks. File control block FCB has information about a file — owner, size, permissions, location of file contents. Advantages :. Next File Systems in Operating System. Recommended Articles. Article Contributed By :. Easy Normal Medium Hard Expert. Writing code in comment? Please use ide.

The file system also doesn't allow creating files the size of which exceeds 4 GB. To address this issue, exFAT was introduced, which doesn't have any realistic limitations concerning the size and is frequently utilized on modern external hard drives and SSDs.

Most operating systems of the Windows Server line use this format as well. This FS type is quite reliable thanks to journaling and supports many features, including access control , encryption, etc. The Master file table contains entries with all information about them: size, allocation, name, etc. The first 16 entries of the table are retained for the BitMap, which keeps record of all free and used clusters, the Log used for journaling records and the BadClus containing information about bad clusters.

The first and the last sectors of the file system contain its settings the boot record or the superblock. This format uses 48 and 64 bit values to reference files, thus being able to support data storages with extremely high capacity. ReFS has high tolerance to failures due to new features included into it. The most noteworthy one among them is Copy-on-Write CoW : no metadata is modified without being copied; data is not written over the existing data — it is placed to another area on the disk.

After any modifications, a new copy of metadata is saved to a free area on the storage, and then the system creates a link from older metadata to the newer copy. Thus, a significant quantity of older backups are stored in different places, providing easy data recovery unless this storage space is overwritten. In contrast to FAT, which simply allocates any first free cluster on the disk for the file fragment, HPFS seeks to arrange the file in contiguous blocks, or at least ensure that its fragments referred to as extents are placed maximally close to each other.

At the beginning of HPFS, there are three control blocks occupying 18 sectors: the boot block , the super block and the spare block.

The remaining storage space is divided into parts of contiguous sectors referred to as bands taking 8 MB each. A band has its own sector allocation bitmap showing which sectors in it are occupied 1 — taken, 0 — free. Each file and directory has its own F-Node located close to it on the disk — this structure contains the information about the location of a file and its extended attributes.

A special directory band located in the center of the disk is used for storing directories, while the directory structure itself is a balanced tree with alphabetical entries. Hint: The information concerning data recovery perspectives of the FS types used by Windows can be found in the articles on data recovery specificities of different OS and chances for data recovery.

For detailed instructions and recommendations, please, read the manual devoted to data recovery from Windows. Volumes are divided into sectors, typically bytes in size, then they are grouped into allocation blocks, the number of which depends on the size of the entire volume. The information concerning free and used allocation blocks is kept in the Allocation File.

All allocation blocks assigned to each file as extends are recorded in the Extends Overflow File. And, finally, all file attributes are listed in the Attributes file.

Data reliability is improved through journaling which makes it possible to keep track of all changes to the system and quickly return it back to the working state in case of unexpected events.

Among other supported features are hard links to directories, logical volume encryption, access control, data compression, etc. The Apple file system is aimed to address fundamental issues present in its predecessor and was developed to efficiently work with modern flash storages and solid-state drives. This bit format uses the copy-on-write method to increase performance, which allows to copy each block before the changes to it are applied, and offers a lot of data integrity and space-saving features.

The Container Superblock stores information about the number of blocks in the Container, the block size, etc. Information about all allocated and free blocks of the Container is managed with the help of Bitmap Structures.

Each volume in the Container has its own Volume Superblock which provides information about this volume. All files and folders of the volume are recorded in the File and Folder B-Tree , while the Extents B-Tree is responsible for extents — references to file contents file start, its length in blocks. Hint: The details related to the possibility of data recovery from these FS types can be found in the articles about the peculiarities of data recovery depending on the operating system and chances for data recovery.

Open-source Linux aims at implementing, testing and using different types of file systems. The most popular formats for Linux include:. Ext2, Ext3, Ext4 are simply different versions of the "native" Linux Ext file system. This type falls under active developments and improvements. These text-based interfaces help users do all sorts of file operations as text commands - Like how we did in the previous examples.

This feature is also available in the CLI Command prompt or Terminal , where a user can change file ownerships or limit permissions of each file right from the command line interface. For instance, a file owner on Linux or Mac can configure a file to be available to the public, like so:. Please note this is just an example, and you should not set a file's permission to One day, you open the file, make some changes and save it.

But what if the system crashes while the older version of the file is being replaced with the new version? In older file systems like FAT32 or ext2 the data would be corrupted because it was partially written to the disk. This is less likely to happen with modern file systems as they use a technique called journaling.

The main purpose is to keep track of the changes that haven't yet been committed to the file system physically. The journal is a special allocation on the disk where each writing attempt is first stored as a transaction. Once the data is physically placed on the storage device, the change is committed to the filesystem. In case of a system failure, the file system will detect the incomplete transaction and roll it back as if it never happened. That said, the new content that was being written may still be lost, but the existing data would remain intact.

The database file system is a faceted system which groups files based on various attributes and dimensions. For instance, MP3 files can be listed by artist, genre, release year, and album - at the same time! A database file system is more like a high-level application to help you organize and access your files more easily and more efficiently. A database file system cannot replace a typical file system, though. You made it to the end, which means you know a lot more about file systems now.

But I'm sure this won't be the end of your file system studies. A file system defines how files are named , stored , and retrieved from the storage device. Alright, I think it does it for this write-up. If you notice something is missing or that I've gotten wrong, please let me in the comments below. That would help me and others too! By the way, if you like more comprehensive guides like this one, visit my website decodingweb.

I enjoy helping people including myself decode the complex side of technology. If you read this far, tweet to the author to show them you care. Tweet a thanks. Learn to code for free. Get started. Forum Donate. Reza Lavarian. It's a bit tricky to explain what exactly a file system is in just one sentence. Let's start with a simple definition: A file system defines how files are named , stored , and retrieved from a storage device.

Or when you copy, edit, or delete a file, the file system handles it under the hood. However, these concepts remain relevant to other environments and file systems.

Why do we need a file system in the first place, you may ask? Imagine a room with piles of papers scattered all over the place. However, a file system changes everything: A file system isn't just a bookkeeping feature, though. Everything begins with partitioning Storage devices must be partitioned and formatted before the first use. But what is partitioning? A storage device should have at least one partition or more if needed. Why should we split the storage devices into multiple partitions anyways?

The recovery and diagnostic utilities reside in dedicated partitions too. For instance, the tech team would appreciate a quieter area. Are you ready? Away we go! Wait, what is the system firmware? You may ask. Here's an explanation: A firmware is a low-level software embedded into electronic devices to operate the device, or bootstrap another program to do it.

This sector is called MBR. MBR contains the following information: The boot loader, which is a simple program in machine code to initiate the first stage of the booting process A partition table , which contains information about your partitions. MBR gap can be used to place another piece of the boot loader program if needed.

This is when the operating system's logo fades in MBR's data structure limits the number of partitions to only four primary partitions. When making a partition, you can choose between primary and extended. After this is solved, we'll encounter the second limitation. And wait, there's more! For instance, you can have as many partitions as your operating system allows. This is where the first-stage boot loader would reside in an MBR-partitioned disk After this first sector, the GPT data structures are stored, including the GPT header and the partition entries.

This backup is called Secondary GPT. If this path cannot be found on your system, then your firmware is probably BIOS-based firmware.

NVRAM contains the booting settings and paths to the operating system boot loader files. Let's confirm that with the dmidecode command like so: sudo dmidecode -t 0 And the output would be: dmidecode 3. Formatting partitions When partitioning is done, the partitions should be formatted. Most operating systems allow you to format a partition based on a set of file systems.

These data structures are one aspect of a file system. Let's take the NTFS file system as an example. How it started, how it's going A file system is a set of data structures, interfaces, abstractions, and APIs that work together to manage any type of file on any type of storage device, in a consistent manner.

Each operating system uses a particular file system to manage the files. Or you can just use the exFat file system. But how about file systems in Linux distributions? When people talk about file systems, they refer to one of these layers or all three as one unit. Although these layers are different across operating systems, the concept is the same. The next layer is the virtual file system or VFS. So does this mean an operating system can use multiple file systems at the same time?

The answer is yes! Can you guess what it is? Yes, we're talking about the logical file system. A high-level architecture of the file system layers What does it mean to mount a file system? However, there are times you need to mount a file system manually. Please note that the mount point should already exist as a directory.

Inodes are identified by a unique number called the inode number. Inodes are associated with files in a table called inode tables. The inode also includes the address of the blocks allocated to the file; On the other hand, where exactly it's located on the storage device In an ext4 inode, the address of the allocated blocks is stored as a set of data structures called extents within the inode.

Whenever you open a file on Linux, its name is first resolved to an inode number. Having the inode number, the file system fetches the respective inode from the inode table.

On NTFS, the metadata is stored differently, though. On most operating systems, you can grab metadata via the graphical user interface. Space Management Storage devices are divided into fixed-sized blocks called sectors. Depending on the file size, the file system allocates one or more blocks to each file.

The layout of a block group within an ext4 partition Each block group has its own data structures and data blocks. Here are the data structures a block group can contain: Super Block: a metadata repository, which contains metadata about the entire file system, such as the total number of blocks in the file system, total blocks in block groups, inodes, and more.

Not all block groups contain the superblock, though. A certain number of block groups store a copy of the super as a backup.