f2fs

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      F2FS (Flash-Friendly File System) is a flash file system initially developed by Samsung Electronics for the Linux kernel.
      The motive for F2FS was to build a file system that, from the start, takes into account the characteristics of NAND flash memory-based storage devices (such as solid-state disks, eMMC, and SD cards), which are widely used in computer systems ranging from mobile devices to servers.
      F2FS was designed on a basis of a log-structured file system approach, which is adapted to newer forms of storage. Jaegeuk Kim, the principal F2FS author, has stated that it remedies some known issues of the older log-structured file systems, such as the snowball effect of wandering trees and high cleaning overhead. In addition, since a NAND-based storage device shows different characteristics according to its internal geometry or flash memory management scheme (such as the Flash Translation Layer or FTL), it supports various parameters not only for configuring on-disk layout, but also for selecting allocation and cleaning algorithms.
      Note, that by default F2FS uses "posix" fsync scheme, which carries higher risks of leaving the file system in dirty state during unclean shutdown (as it does not guarantee atomicity of write operations) at the benefit of better performance. There is a more stringent method that respects hardware limitations for greater security at the expense of performance; see the "fsync_mode" option in the manual for details.


      Features


      Multi-head logging
      Multi-level hash table for directory entries
      Static/dynamic hot and cold data separation
      Adaptive logging scheme
      Configurable operational units
      Dual checkpoint
      Roll-back and roll-forward recovery
      Heap-style block allocation
      TRIM/FITRIM support
      Online fs defragmentation/file defragmentation
      Inline xattrs/data/dir
      Offline filesystem check (Check and fix inconsistency)
      Atomic operations
      Filesystem-level encryption
      Offline resizing (shrinking not supported.)
      Inner periodically data flush
      Extent cache
      Transparent file compression using LZO or LZ4 (with Linux 5.6), or zstd (with Linux 5.7)


      Design




      = On-disk layout

      =
      F2FS divides the whole volume into a number of segments, each of which is fixed at 2 MB. A section is composed of consecutive segments, and a zone consists of a set of sections. By default, section and zone sizes are set to the same size, but users can easily modify the size with mkfs.
      F2FS splits the entire volume into six areas, and all except the superblock area consist of multiple segments as described below.

      Superblock (SB)
      The SB is located at the beginning of the partition. There are two copies to avoid file-system corruption. It contains basic partition information and some default F2FS parameters.
      Checkpoint (CP)
      The CP contains file system information, bitmaps for valid NAT/SIT sets, orphan inode lists, and summary entries of current active segments.
      Segment Information Table (SIT)
      The SIT contains the valid block count and validity bitmap of all the Main Area blocks.
      Node Address Table (NAT)
      The NAT is an address table for the Main Area node blocks.
      Segment Summary Area (SSA)
      The SSA contains entries which contain the owner information of the Main Area data and node blocks.
      Main Area
      The main area contains file and directory data and their indices.
      In order to avoid misalignment between file system and flash storage, F2FS aligns the start block address of the CP with the segment size. It also aligns the Main Area start block address with the zone size by reserving some segments in the SSA area.


      = Metadata structure

      =
      F2FS uses the checkpoint scheme to maintain file system integrity. At mount time, F2FS first tries to find the last valid checkpoint data by scanning the CP area. In order to reduce the scanning time, F2FS uses only two copies of the CP. One of them always indicates the last valid data, which is called a shadow copy mechanism. In addition to the CP, the NAT and SIT also use the shadow copy mechanism. For file system consistency, each CP points to which NAT and SIT copies are valid.


      = Index structure

      =
      The key data structure is the "node". Similar to traditional file structures, F2FS has three types of nodes: inode, direct node, indirect node. F2FS assigns 4 KB to an inode block which contains 923 data block indices, two direct node pointers, two indirect node pointers, and one double indirect node pointer as described below. A direct node block contains 1018 data block indices, and an indirect node block contains 1018 node block indices. Thus, one inode block (i.e., a file) covers:

      4 KiB × (923 + 2×1018 + 2×10182 + 10183) = 4,228,213,756 KiB = 4,129,114.996 MiB = 4,032.338863 GiB = 3.937830921 TiB

      Note that all the node blocks are mapped by the NAT, which means that the location of each node is translated by the NAT. To mitigate the wandering tree problem, F2FS is able to cut off the propagation of node updates caused by leaf data writes.


      = Directory structure

      =
      A directory entry (dentry) occupies 11 bytes, which consists of the following attributes.

      A dentry block consists of 214 dentry slots and file names. A bitmap is used to represent whether each dentry is valid or not. A dentry block occupies 4 KB and has the following composition:

      Dentry Block (4 K) = bitmap (27 bytes)
      + reserved (3 bytes)
      + dentries (11 * 214 bytes)
      + file name (8 * 214 bytes)

      F2FS implements multi-level hash tables for the directory structure. Each level has a hash table with a dedicated number of hash buckets as shown below. Note that "A(2B)" means a bucket includes 2 data blocks.

      Term
      A indicates bucket
      B indicates block
      N indicates MAX_DIR_HASH_DEPTH
      level #0 A(2B)
      level #1 A(2B) - A(2B)
      level #2 A(2B) - A(2B) - A(2B) - A(2B)
      ...
      level #N/2 A(2B) - A(2B) - A(2B) - A(2B) - A(2B) - ... - A(2B)
      ...
      level #N A(4B) - A(4B) - A(4B) - A(4B) - A(4B) - ... - A(4B)

      When F2FS finds a file name in a directory, first a hash value of the file name is calculated. Then, F2FS scans the hash table in level #0 to find the dentry consisting of the file name and its inode number. If not found, F2FS scans the next hash table in level #1. In this way, F2FS scans hash tables in each level incrementally from 1 to N. In each level F2FS needs to scan only one bucket determined by the following equation, which shows O(log(# of files)) complexity.

      bucket number to scan in level #n = (hash value) % (# of buckets in level #n)

      In the case of file creation, F2FS finds empty consecutive slots that cover the file name. F2FS searches the empty slots in the hash tables of whole levels from 1 to N in the same way as the lookup operation.


      = Default block allocation

      =
      At runtime, F2FS manages six active logs inside the "Main Area:" Hot/Warm/Cold node and Hot/Warm/Cold data.

      LFS has two schemes for free space management: threaded log and copy-and-compaction. The copy-and-compaction scheme which is known as cleaning, is well-suited for devices showing very good sequential write performance, since free segments are served all the time for writing new data. However, it suffers from cleaning overhead during high utilization. Conversely, the threaded log scheme suffers from random writes, but no cleaning process is needed. F2FS adopts a hybrid scheme where the copy-and-compaction scheme is adopted by default, but the policy is dynamically changed to the threaded log scheme according to the file system status.
      In order to align F2FS with underlying flash-based storage, F2FS allocates a segment in a unit of a section. F2FS expects the section size to be the same as the garbage collection unit size in FTL. With respect to the mapping granularity in FTL, F2FS allocates each section of the active logs to as many different zones as possible. FTL can write the active log data into one allocation unit according to its mapping granularity.


      = Cleaning process

      =
      F2FS does cleaning both on demand, and in the background. On-demand cleaning is triggered when there are not enough free segments to serve VFS calls. The background cleaner is executed by a kernel thread, and triggers the cleaning job when the system is idle.
      F2FS supports two victim selection policies: greedy, and cost-benefit algorithms. In the greedy algorithm, F2FS selects a victim segment having the smallest number of valid blocks. In the cost-benefit algorithm, F2FS selects a victim segment according to the segment age and the number of valid blocks in order to address the log block thrashing problem present in the greedy algorithm. F2FS uses the greedy algorithm for on-demand cleaning, the background cleaner uses the cost-benefit algorithm.
      In order to identify whether the data in the victim segment are valid or not, F2FS manages a bitmap. Each bit represents the validity of a block, and the bitmap is composed of a bit stream covering whole blocks in the Main Area.


      Adoption




      = Phone manufacturers

      =
      Google first used F2FS in their Nexus 9 in 2014.

      However Google's other products didn't adopt F2FS until the Pixel 3 when F2FS was updated with inline crypto hardware support.

      Huawei has used F2FS since the Huawei P9 in 2016.

      OnePlus has used F2FS in the OnePlus 3T.
      Motorola Mobility has used F2FS in their Moto G/E/X and Droid phones since 2012.
      ZTE has used F2FS since the ZTE Axon 10 Pro in 2019.


      = Linux distributions

      =
      F2FS has been merged into Linux kernel in late 2012. Many distributions support it.


      See also


      Comparison of file systems
      List of flash file systems


      References




      External links


      FAST '15 - F2FS: A New File System for Flash Storage (2015-02-17)
      WHAT IS Flash-Friendly File System (F2FS) documentation for Linux
      Flash Friendly File System (F2FS), Embedded Linux Conference (2013-02-22)
      LWN.net: An f2fs teardown (2012-10-10)
      eMMC/SSDFile SystemTuningMethodology (2013-05-24)

    Kata Kunci Pencarian: f2fs

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    f2fs

    Daftar Isi

    How do you decrypt an f2fs partition? - Unix & Linux Stack …

    Apr 4, 2024 · f2fs-tools version f2fs-tools/mantic,now 1.16.0-1 Using twrp is not an option, it fails to decrypt it via the shell and the screen is broken. I need to be able to decrypt it on my computer.

    Why isn't F2FS a thing? : r/linux - Reddit

    F2FS has the same resilience mechanisms as FAT32: almost none. If a power outage or kernel crash happens when writing into filesystem data, there are no ways to recover it and even no ways to detect if the damage was done. It is the reason why F2FS is fast: no upkeeping tasks. I bet FAT32 would be just as fast in those tests, but noone uses it too.

    Changed from f2fs to ext4 : r/archlinux - Reddit

    Jul 4, 2023 · On write performance, EXT4 seems to outperform F2FS ONLY when working with small files. And F2FS performs just a little bit better with larger files. So purely based on numbers, my "feeling" of EXT4 being faster than F2FS is subjective. Below you can find the 2 chart images with the comparison, as well as the txt files returned by kdiskmark.

    How is the maximum volume size supported by the F2FS file …

    Aug 10, 2020 · The storage device is divided into blocks of size 4096 bytes. The block addresses are 32 bits in size, which results in a maximum size of 2^32 * 4096 bytes = 16 TB.

    How To F2FS Filesystem Encryption? - Unix & Linux Stack …

    Dec 25, 2016 · @xendi You can use LUKS with F2FS. You create the LUKS container first and then the filesystem, just like with any other filesystem. LUKS does work with TRIM and it doesn't “make F2FS useless”. The point of encryption on top of F2FS is if you want per-file encryption, i.e. if you don't want full disk encryption. –

    encryption - How to encrypt a file or a folder on f2fs? - Unix

    Oct 26, 2017 · Install the user space tools for the f2fs filesystem: root #emerge --ask sys-fs/f2fs-tools After emerging the userspace tools, create a filesystem by running the mkfs.f2fs command followed by the appropriate device and partition number: root #mkfs.f2fs /dev/sdd1

    F2FS: show options on existing partition/add to existing partition ...

    Jan 18, 2021 · Re: F2FS: show options on existing partition/add to existing partition I ended up copying everything off the partition and re-creating it with those options. I did not look under /sys/fs/f2fs/features initially, only under /sys/fs/f2fs/dm-0 .

    F2FS on a SATA SSD : r/archlinux - Reddit

    Dec 23, 2021 · I'm using F2FS on arch linux from 2years. I started with Manjaro but now it looks more stable and speedy if you're using 5.14 + kernel. I also tried traditional FS but never got such speed and performance. Give F2FS a try on Arch Linux.

    SSD Filesystem: XFS vs F2FS vs Btrfs vs Bcachefs vs ext4

    May 29, 2023 · AFAIK the dedicated flash FSs like F2FS are meant for devices where the FS has direct control over the physical sectors. On drives that present virtual sectors to the OS and control the physical sectors themselves in firmware (wear leveling) flash filesystems have no effect. That should probably be every SATA or NVME SSD.

    How to enble quota option f2fs filesystem?

    Dec 29, 2021 · Find the line corresponding to your f2fs filesystem. Add the usrquota and grpquota options (or prjquota for project quotas) to the mount options. For example: /dev/sdX1 /path/to/mountpoint f2fs defaults,usrquota,grpquota 0 0 Save the file and remount the filesystem with sudo mount -o remount /path/to/mountpoint Using the mount command: