APFS: near-and-far metadata

[pjotrek-b]

According to An Article on eclecticlight.co about APFS/xattrs, there are 2 ways xattrs are stored:

Quote:

• In APFS, xattrs are stored outside the inode and its attributes, and separate from a file’s data.
• Data for smaller xattrs of up to 3,804 bytes is stored with the xattr in the file system metadata.
• Data for larger xattrs is stored as data streams, with separate records.

Which means:

1. meta-and-data are addressable "as one", but stored separately, allowing to speed-tune them separately (eg HDDs vs SSDs vs NVRAM vs RAM).
2. "near" metadata: up to 3,804 bytes.
3. "far" metadata: larger than 4 kB: individual data streams (like auto-linked sidecar files).

Sounds quite beautiful!

[pjotrek-b]

This I'd use like this:

• "embedded metadata, usually < 3kB" goes "near"
• CSV, JSON, XML, and any other extended metadata (>4kB) goes "separate streams", and stays related by identifier.