Computer file system

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 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.

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. That would help me and others too! By the way, if you like more comprehensive guides like this one, visit my website decodingweb. Source link. Save my name, email, and website in this browser for the next time I comment. Code your own Netflix clone! We just published a course on the freeCodeCamp.

It turns off. Are you hyped about augmented reality?! Solution Architecture! The Open Group definition of solution architecture has. Flutter and Firebase can work well together to create a full stack app. No products in the cart. Websites Coming Soon. Coming Soon. Quick View. Email Templates. E-commerce product promotional. Add to cart. Responsive podcasting email. Responsive Deforestation email. Simple quick survey. Pricing table Dashboard Login page Button menu. What Is a File System? Tamim Hasan January 11, No Comments.

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. 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. 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. When making a partition, you can choose between primary and extended. 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. 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. 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?

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. 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.

Group Descriptors: Group descriptors also contain bookkeeping information for each block group Inode Bitmap: Each block group has its own inode quota for storing files.

A block bitmap is a data structure used to identify used and unused inodes within the block group. The number of inodes stored in this area is related to the block size used by the file system.

Data Blocks: This is the zone within the block group where file contents are stored. The layout of the first block group looks like this: The layout of the first block in an ext4 flex block group When a file is being written to a disk, it is written to one or more blocks within a block group.

Size vs size on disk Have you ever noticed that your file explorer displays two different sizes for each file: size, and size on disk. Size and Size on disk Why are size and size on disk slightly different?

You can use the du command on Linux to see it yourself. What is disk fragmentation? Over time, new files are written to the disk, existing files get bigger, shrunk, or deleted. Imagine you have a Word document named myfile. This overhead applies to saving the file back to the disk as well. Fragmentation is one of the reasons some operating systems get slow as the file system ages.

Should We Care About Fragmentation these days? The short answer is: not anymore! Additionally, ext4 uses an allocation technique called delayed allocation.

Delayed allocation actively reduces fragmentation and increases performance. Directories A Directory Folder in Windows is a special file used as a logical container to group files and directories within a file system. On Linux, you can use the ls in a directory to see the directory entries with their associated inode numbers: ls -lai And the output would be something like this: drwxr-xr-x 14 root root Dec 1 Rules for naming files Some file systems enforce limitations on filenames.

Why does this matter? So keep that in mind when developing on Windows and deploying to a Linux server. Rules for file size One important aspect of file systems is the maximum file size they support. File manager programs As you know, the logical layer of the file system provides an API to enable user applications to perform file operations, such as read , write , delete , and execute operations.

For instance, a file owner on Linux or Mac can configure a file to be available to the public, like so: chmod myfile. The request is eventually passed down to the physical layer to store the file on several blocks. Database File Systems Typical file systems organize files as directory trees. The iTunes app on Mac OS is a good example of a database file system. Wrapping Up Wow! So again — can we describe what a file system is and how it works in one sentence?

Thanks for reading, and enjoy learning! Leave Your Comment Cancel Reply. January 13, No Comments. January 12, No Comments. Storage devices must be partitioned and formatted before the first use. Partitioning is splitting a storage device into several logical regions , so they can be managed separately as if they are separate storage devices.

We usually do partitioning by a disk management tool provided by operating systems, or as a command-line tool provided by the system's firmware I'll explain what firmware is. The reason is that we don't want to manage the whole storage space as a single unit and for a single purpose.

It's just like how we partition our workspace, to separate and isolate meeting rooms, conference rooms, and various teams. For example, a basic Linux installation has three partitions: one partition dedicated to the operating system, one for the users' files, and an optional swap partition.

Operating systems continuously use various memory management techniques to ensure every process has enough memory space to run. File systems on Windows and Mac have a similar layout, but they don't use a dedicated swap partition; Instead, they manage to swap within the partition on which you've installed your operating system. On a computer with multiple partitions, you can install several operating systems, and every time choose a different operating system to boot up your system with.

By doing so, you instruct the system's firmware to boot up with a partition that contains the recovery program. Partitioning isn't just a way of installing multiple operating systems and tools, though; It also helps us keep critical system files apart from ordinary ones. So no matter how many games you install on your computer, it won't have any effect on the operating system's performance - since they reside in different partitions.

Back to the office example, having a call center and a tech team in a common area would harm both teams' productivity because each team has its own requirements to be efficient.

For instance, the primary partition on Windows on which Windows is installed is known as C :, or drive C. In Unix-like operating systems, however, partitions appear as ordinary directories under the root directory - we'll cover this later.

In the next section, we'll dive deeper into partitioning and get to know two concepts that will change your perspective on file systems: system firmware and booting. Regardless of what partitioning scheme you choose, the first few blocks on the storage device will always contain critical data about your partitions.

The system's firmware uses these data structures to boot up the operating system on a partition. A firmware is a low-level software embedded into electronic devices to operate the device, or bootstrap another program to do it.

Firmware exists in computers, peripherals keyboards, mice, and printers , or even electronic home appliances. In computers, the firmware provides a standard interface for complex software like an operating system to boot up and work with hardware components.

However, on simpler systems like a printer, the firmware is the operating system. The menu you use on your printer is the interface of its firmware. The mission of the firmware among other things is to boot up the computer, run the operating system, and pass it the control of the whole system. A firmware also runs pre-OS environments with network support , like recovery or diagnostic tools, or even a shell to run text-based commands. The first few screens you see before your Windows logo appears are the output of your computer's firmware, verifying the health of hardware components and the memory.

The initial check is confirmed with a beep usually on PCs , indicating everything is good to go. On MBR-partitioned disks, the first sector on the storage device contains essential data to boot up the system. Once the program is on the memory, the CPU begins executing it. Having the boot loader and the partition table in a predefined location like MBR enables BIOS to boot up the system without having to deal with any file. If you are curious about how the CPU executes the instructions residing in the memory, you can read this beginner-friendly and fun guide on how the CPU works.

Additionally, 64 bytes are allocated to the partition table, which can contain information about a maximum of four partitions.

That said, sophisticated boot loaders like GRUB 2 on Linux split their functionality into pieces or stages. The smallest piece of code known as the first-stage boot loader is stored in the MBR. It's usually a simple program, which doesn't require much space. The responsibility of the first-stage boot loader is to initiate the next and more complicated stages of the booting process.

GRUB calls this the stage 1. Stage 1. The second stage boot loader, which is now capable of working with files, can load the operating system's boot loader file to boot up the respective operating system. A common workaround is to make an extended partition beside the primary partitions, as long as the total number of partitions won't exceed four. An extended partition can be split into multiple logical partitions.

Making extended partitions is different across operating systems. Over this quick guide Microsoft explains how it should be done on Windows. And every partition can be the size of the biggest storage device available in the market - actually a lot more. This sector is called Protective MBR. This is where the first-stage boot loader would reside in an MBR-partitioned disk.

The GPT entries and the GPT header are backed up at the end of the storage device, so they can be recovered if the primary copy gets corrupted. Once the EFI partition is found, it looks for the configured boot loader - usually, a file ending with. You can use the parted command on Linux to see what partitioning scheme is used for a storage device.

Formatting involves the creation of various data structures and metadata used to manage files within a partition. Alright, let's get back file systems with our new background about partitioning, formatting, and booting. 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.

Starting from Windows NT 3. So basically, if you have a removable disk you want to use on Windows, Mac, and Linux, you need to format it to exFAT. The Extended File System ext family of file systems was created for the Linux kernel - the core of the Linux operating system. The first version of ext was released in , but soon after, it was replaced by the second extended file system ext2 in In the s, the third extended filesystem ext3 and fourth extended filesystem ext4 were developed for Linux with journaling capability.

The physical layer is the concrete implementation of a file system; It's responsible for data storage and retrieval and space management on the storage device or precisely: partitions. The physical file system interacts with the storage hardware via device drivers. The virtual file system provides a consistent view of various file systems mounted on the same operating system. It's common for a removable storage medium to have a different file system than that of a computer.

For instance, when you open up your file explorer program, you can copy an image from an ext4 file system and paste it over to your exFAT-formatted flash memory - without having to know that files are managed differently under the hood. This convenient layer between the user you and the underlying file systems is provided by the VFS. A VFS defines a contract that all physical file systems must implement to be supported by that operating system.

However, this compliance isn't built into the file system core, meaning the source code of a file system doesn't include support for every operating system's VFS. Instead, it uses a file system driver to adhere to the VFS rules of every file system. A driver is a program that enables software to communicate with another software or hardware. Although VFS is responsible for providing a standard interface between programs and various file systems, computer programs don't interact with VFS directly.

On the other hand, VFS provides a bridge between the logical layer which programs interact with and a set of the physical layer of various file systems. Then, it creates a virtual directory tree and puts the content of each device under that directory tree as separate directories. The act of assigning a directory to a storage device under the root directory tree is called mounting , and the assigned directory is called a mount point.

That said, on a Unix-like operating system, all partitions and removable storage devices appear as if they are directories under the root directory. If the mount-point directory already contains files, those files will be hidden for as long as the device is mounted. In Unix-like systems, the metadata is in the form of data structures, called inode. Each file on the storage device has an inode, which contains information about it such as the time it was created, modified, etc.

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. Each extent contains the address of the first data block allocated to the file and the number of the continuous blocks that the file has occupied.

Once the inode is fetched, the file system starts to compose the file from the data blocks registered in the inode. You can use the df command with the -i parameter on Linux to see the inodes total, used, and free in your partitions:. To see the inodes associated with files in a directory, you can use the ls command with -il parameters. The number of inodes on a partition is decided when you format a partition. That said, as long as you have free space and unused inodes, you can store files on your storage device.

It's unlikely that a personal Linux OS would run out of inodes. However, enterprise services that deal with a large number of files like mail servers have to manage their inode quota smartly. Every file has at least one entry in MFT, which contains everything about it, including its location on the storage device - similar to the inodes table. For instance, when you right-click on a file on Mac OS, and select Get Info Properties in Windows , a window appears with information about the file.

A sector is the minimum storage unit on a storage device and is between bytes and bytes Advanced Format. However, file systems use a high-level concept as the storage unit, called blocks. Blocks are an abstraction over physical sectors; Each block usually consists of multiple sectors. The most basic storage unit in ext4-formatted partitions is the block.

However, the contiguous blocks are grouped into block groups for easier management. Ext4 file system even takes one step further comparing to ext3 , and organizes block groups into a bigger group called flex block groups. The data structures of each block group, including the block bitmap, inode bitmap, and inode table, are concatenated and stored in the first block group within each flex block group.

Having all the data structures concatenated in one block group the first one frees up more contiguous data blocks on other block groups within each flex block group. These concepts might be confusing, but you don't have to master every bit of them. It's just to depict the depth of file systems. When a file is being written to a disk, it is written to one or more blocks within a block group. Managing files at the block group level improves the performance of the file system significantly, as opposed to organizing files as one unit.

Have you ever noticed that your file explorer displays two different sizes for each file: size, and size on disk. One block is the minimum space that can be allocated to a file. This means the remaining space of a partially-filled block cannot be used by another file. This is the rule! Since the size of the file isn't an integer multiple of blocks , the last block might be partially used, and the remaining space would remain unused - or would be filled with zeros. Based on the output, the allocated block is about 4kb, while the actual file size is bytes.

This means each block size on this operating system is 4kb. These frequent changes in the storage medium leave many small gaps empty spaces between files. These gaps are due to the same reason file size and file size on disk are different. Some files won't fill up the full block, and lots of space will be wasted.

And over time there' won't be enough consequent blocks to store new files. File Fragmentation occurs when a file is stored as fragments on the storage device because the file system cannot find enough contiguous blocks to store the whole file in a row.

Now, if you add more content to myfile. Since myfile. In that case, the new content of myfile. File fragmentation puts a burden on the file system because every time a fragmented file is requested by a user program, the file system needs to collect every piece of the file from various locations on a disk. The fragmentation might also occur when a file is written to the disk for the first time, probably because the file is huge and not many continuous blocks are left on the partition.

Modern file systems use smart algorithms to avoid or early-detect fragmentation as much as possible. Ext4 also does some sort of preallocation, which involves reserving blocks for a file before they are actually needed - making sure the file won't get fragmented if it gets bigger over time. The number of the preallocated blocks is defined in the length field of the file's extent of its inode object.

The idea is instead of writing to data blocks one at a time during a write, the allocation requests are accumulated in a buffer and are written to the disk at once. Not having to call the file system's block allocator on every write request helps the file system make better choices with distributing the available space. For instance, by placing large files apart from smaller files.

Imagine that a small file is located between two large files. Now, if the small file is deleted, it leaves a small space between the two files. Spreading the files out in this manner leaves enough gaps between data blocks, which helps the filesystem manage and avoid fragmentation more easily. A Directory Folder in Windows is a special file used as a logical container to group files and directories within a file system. The inode or MFT entry of a directory contains information about that directory, as well as a collection of entries pointing to the files "under" that directory.

The files aren't literally contained within the directory, but they are associated with the directory in a way that they appear as directory's children at a higher level, such as in a file explorer program. These entries are called directory entries.

In addition to the directory entries, there are two more entries. On Linux, you can use the ls in a directory to see the directory entries with their associated inode numbers:. The limitation can be in the length of the filename or filename case sensitivity. The web page contains your company logo, which is a PNG file, like this:. If the actual file name is Logo. Because in Linux ext4 file system logo. This makes exFAT an ideal option for storing massive data objects, such as video files.

As you know, the logical layer of the file system provides an API to enable user applications to perform file operations, such as read , write , delete , and execute operations. That said, operating systems provide convenient file management utilities out of the box for your day-to-day file management. 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:.