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Samsung Creates New File System F2Fs For Linux & Android

Posted by Soulskill on from the file-systems-are-for-files dept.

sfcrazy writes "Samsung has created a new Linux file system called F2FS. Jaegeuk Kim of Samsung writes on the Linux Kernel Mailing List: F2FS is a new file system carefully designed for the NAND flash memory-based storage devices. We chose a log structure file system approach, but we tried to adapt it to the new form of storage. Also we remedy some known issues of the very old log structured file system, such as snowball effect of wandering tree and high cleaning overhead."

3 of 140 comments (clear)

  1. Re:SSD Drives by Anonymous Coward · · Score: 5, Informative

    No. SSDs present themselves to the OS as contiguous block devices. Filesystems intended for bare NAND flash like jffs(2), yaffs, and this new F2Fs would be totally useless for SSDs. They're intended for bare NAND, which SSDs are not.

  2. It's not for bare NAND by bogolisk · · Score: 5, Informative

    No. SSDs present themselves to the OS as contiguous block devices. Filesystems intended for bare NAND flash like jffs(2), yaffs, and this new F2Fs would be totally useless for SSDs. They're intended for bare NAND, which SSDs are not.

    You're wrong

    f2fs work on top of block devices. f2fs sends TRIM (ATA command) down to the device. Bare NAND flash doesn't grok ATA commands.

    --
    Bogus
    1. Re:It's not for bare NAND by romiz · · Score: 5, Informative

      The problem is that even with a translation layer for block access, flash-based devices have limitations, which means that different usage patterns can dramatically change the performance of the device.

      For a (simplified) example, to write a file in ext3, you need to store the new data for the file, but you also need to store other metadata: the location of the data blocks themselves in the inode, the file size in the directory, the journaling data. This means that you have four 'internal block descriptors' open for writing at the same time.

      But block descriptors are a limited resource in SSDs, and even more so for low-cost eMMC devices. This means that with only two or three open files with regular writing, you could quite easily lead to some kind of thrashing state, with the device quickly opening and closing descriptors. Since flash memory writing is strongly constrained, this means that a whole block (2 MiB block size is common) containing a descriptor will need to be erased before its next use. As a result, each block only contains little interesting data, and writing only a small amount of data leads to a lot of flash write and erase access. This problem is called write amplification, and reduces both the disk's performance and its durability.

      The F2FS design is a log-based design, where all files on the disk share 6 common writing areas, for each kind of stored data, where the information is stored as it arrives. This will have a very positive effect against the write amplification problem, and is an example of how an adapted file system can have a positive impact, even on block-based devices.