diff --git a/docs/faq.rst b/docs/faq.rst
index e3de4bf95d9..5fc3a83a2a7 100644
--- a/docs/faq.rst
+++ b/docs/faq.rst
@@ -357,6 +357,16 @@ to change them.
 
 Use ``borg repo-compress`` to efficiently recompress a complete repository.
 
+Why is backing up an unmodified FAT filesystem slow on Linux?
+-------------------------------------------------------------
+
+By default, the files cache used by BorgBackup considers the inode of files.
+When an inode changes compared to the last backup, it hashes the file again.
+The ``vfat`` kernel driver does not produce stable inodes by default. One way
+to achieve stable inodes is mounting the filesystem using ``nfs=nostale_ro``.
+Doing so implies mounting the filesystem read-only. Another option is to not
+consider inodes in the files cache by passing ``--files-cache=ctime,size``.
+
 Security
 ########