Why use the JFS filesystem

September 8, 2018

Lang: cs en de es

When my colleague Martin asked me, "On your blog it says that you use the JFS file system. Could you summarize why you use it and what are its advantages? I don't have JFS anywhere, so I'm interested." I wrote this article about JFS and its benefits.

More about file systems and especially about BTRFS, for which I also offer training on how to use BTRFS, you can read The BTRFS filesystem.

JFS File System

JFS filesystem features:

  • logging for fast data recovery in case of system crash
  • extends to enable a faster filesystem that produces efficient and small file mapping structures;
  • different block sizes of 512, 1024, 2048, 4096 bytes; this will optimize performance;
  • directory organization, where there is a choice between small directories (8 entries or less - their contents are stored in the i-node of the corresponding directory) and large ones (over 8 entries - contents sorted in a balanced tree sorted by name, providing extremely fast access)
  • dynamic allocation of i-nodes; JFS dynamically allocates space for i-nodes as needed, which frees up space that no longer needs to be occupied; all this will avoid reserving fixed disk space for i-nodes during filesystem creation;
  • support for sparse files (i.e. a file that has no data allocated in one or more areas)
More info about JFS on wikipedia.


The information described here is based on a time when there was no EXT4 filesystem, but only EXT3.
Like most users, I did not address the filesystem in the beginning and so had EXT3.


However, what bothered me most about the EXT3 filesystem was the slow checking that is done by fsck. JFS fulfilled my first need, a fast filesystem check, plus it provided other advantages... For example, even today in 2018, one encounters information about the problem of creating files when many are created, thus hitting the limit of the number of inodes. In fact, each new file, link or hardlink needs just one inode. Yet all modern filesystems already have dynamic inode allocation, including JFS.

Since 2014, however, I have been deploying the BTRFS filesystem. which provides additional benefits.

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