Journaling records extra information in case there are problems.
We normally think of our filesystems as a safe place to write information. After working on a document for hours, you want to be able to press save and feel good that your work will still be around when you need it.
But the real story is this isn’t always what happens. If your computer loses power or maybe you’re saving your files to a removable drive and you eject the drive without notice, then you might lose your work.
If that’s not bad enough, the initial problem if left uncorrected could lead to your entire filesystem becoming corrupt. This could cause you to lose information in other files completely unrelated to your recent work.
In order to prevent larger problems like this, filesystems go through checks to make sure they’re in good shape before you can use them. This check is sometimes called fsck in Linux or Mac and chkdsk in Windows. These are the names of the utility applications that do the checking.
Journaling can help prevent this check and help the filesystem recover in case there are problems. But it might not help restore your data.
Listen to the full episode to learn about different types of journals such as a meta-data journal, a data journal, and a write-on-copy journal.