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This article mainly explains "how to enable the ext4 file system in Fedora 9". The content of the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn how to enable the ext4 file system in Fedora 9.

Providing support for the ext4 file system can be said to be the biggest highlight of Fedora 9, but ext4 is only an optional installation. If you enter the installer directly, there is no option for ext4. To enable ext4, you need to press the tab key on the installation startup option after booting the CD, and add the kernel option ext4 on the command line before you can use ext4 during installation. It should be noted that ext4 is still in the dev stage, and Grub does not support ext4 as the boot partition, so if / partition uses ext4, you need to separate the / boot partition and put it on top of the non-ext4 partition, otherwise the system will not be able to boot.

After the CD is booted, press the tab key on the installation startup option, then add the kernel option ext4 to the command line, and the ext4dev option will appear when partitioning.

ABOUT ext4:

Because ext3's inode uses 32 address pointers and 3 indirect pointers, the maximum size of a single file is 2 ^ 10 * 2 ^ 10 * 2 ^ 11, that is, 2 to the 41st power, that is, on a 32 system with 4k blocks, a single file is at most 8TB. Because of the 32-bit address length, ext3 supports a maximum disk size of 2 ^ 31 * 4K, or 8TB (the inode number is a signed int variable, so it is 2 ^ 31).

Due to the development of today's disk arrays, there have been more than 8TB disk arrays, so recently there has been a heated discussion about ext3 extensions in the kernel mailing list, which is ext4.

After a look, the ext3/ext2 developers replaced the original ext3_inode structure with the following inode

Struct ext3_extent {_ _ le32 ee_block; / * first logical block extent covers * / _ _ le16 ee_len; / * number of blocks covered by extent * / _ _ le16 ee_start_hi; / * high 16 bits of physical block * / _ le32 ee_start; / * low 32 bits of physical block * /}

The original inode used 15 pointers to the block in which the file was stored, the last three of which were indirect indexes; now ext4 replaces the original ext3_inode, ext3_extent, with an inode called an extension.

Extent has 3 bytes of space, so the original 15 pointer space can hold 5 extent, and if the files are contiguous enough, you can store files of 5 × 2 ^ 16byte (320kbyte) size. When the original ext3 does not use indirect indexes, it can only store 48kbyte-sized files, so extent reduces the number of small files (medium-sized files?) The number of pointer indexes, speeding up access time

Extent also uses indirect indexes when the file is larger than a certain size, but unlike ext3, extent has no limit on the number of indirect indexes, unlike ext3, which can only do indirect indexes up to 3 times.

Notice the ee_len field, which is 16-bit, which means that one of its chunk groups is 64k, not 4k. This greatly reduces search time, as ext4 developers explain. "now file storage tends to use contiguous blocks, which doesn't cost space."

Another important field is ee_start and ee_start_hi, which together form a 48-bit block index

This can support 1024 PB-sized devices, and in the coming decades, that's enough!

But one drawback of ext4 is that the old kernel does not recognize disks that use ext4.

Thank you for your reading, the above is the content of "how to enable the ext4 file system in Fedora 9". After the study of this article, I believe you have a deeper understanding of how to enable the ext4 file system in Fedora 9, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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