Introduction: The Evolution of Android Partitioning

Modern Android devices, particularly those launching with Android 10 and newer, have moved away from the traditional, fixed-size partitioning scheme. This evolution introduced what are known as Dynamic Partitions, fundamentally changing how storage is managed on a device. This shift is crucial for enabling seamless A/B updates, enhancing storage flexibility, and optimizing resource allocation. At the heart of this new architecture lies the Super Partition and Android’s specialized implementation of Logical Volume Management (LVM).

This article will provide an expert-level deep dive into these concepts, exploring their internal workings, the tools involved, and how they facilitate dynamic resizing and flexible storage for custom ROMs like LineageOS and advanced system modifications.

From Static to Dynamic: A Paradigm Shift

Before Android 10, devices typically had a static partition layout. Partitions like /system, /vendor, /data, and others were allocated fixed blocks of storage on the eMMC or UFS chip. While simple, this approach had significant drawbacks:

• Inflexibility: If the /system partition was too small for a new Android version or a custom ROM, resizing it was often a risky and complex process, sometimes requiring custom tools or image rebuilding.
• Wasted Space: Fixed sizes often led to unused space in one partition while another was critically full.
• A/B Update Challenges: While A/B updates (seamless updates) improved reliability, they still required fixed-size _a and _b slots, doubling the storage commitment for system components.

Dynamic partitions address these issues by abstracting the physical storage. Instead of directly interacting with physical block devices for /system or /vendor, these partitions become logical volumes residing within a larger, physical container: the Super Partition.

The Android Super Partition: The Unified Container

The Super Partition is a single, physical block device (e.g., /dev/block/sde10) that acts as a container for multiple logical partitions. These logical partitions include system, vendor, product, odm, and vbmta (a tiny partition for verifying boot metadata). The /data partition typically remains a separate, static partition.

Key characteristics of the Super Partition:

• It holds the metadata describing the layout and extents of all the logical volumes within it.
• Logical partitions are created as dm-linear devices (device-mapper linear targets), which map ranges of blocks from the Super Partition to a virtual block device (e.g., /dev/block/mapper/system_a).
• dm-verity is often layered on top of these dm-linear devices to ensure the integrity of the read-only partitions like system and vendor.

The metadata for the Super Partition is stored at the beginning of the partition itself, typically within a structure known as super.img. This image contains information about the partition groups (e.g., qcom_update_buffer, default), the logical volumes within those groups, and their sizes and offsets.

Logical Volume Management (LVM) in Android: `liblp` and `lptools`

Android’s LVM implementation is handled by a library called liblp (short for