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3rd chunk of `content/manuals/engine/storage/drivers/zfs-driver.md`
8f34dd92509ed42bf8509e969bdf691fa50b54bccc585e72000000010000095d
The diagram below shows how this is put together with a running container based
on a two-layer image.

![ZFS pool for Docker container](/Users/baehyunsol/Documents/Rust/ragit/sample/docker/content/manuals/engine/storage/drivers/images/zfs_zpool.webp?w=600)

When you start a container, the following steps happen in order:

1.  The base layer of the image exists on the Docker host as a ZFS filesystem.

2.  Additional image layers are clones of the dataset hosting the image layer
    directly below it.

    In the diagram, "Layer 1" is added by taking a ZFS snapshot of the base
    layer and then creating a clone from that snapshot. The clone is writable and
    consumes space on-demand from the zpool. The snapshot is read-only,
    maintaining the base layer as an immutable object.

3.  When the container is launched, a writable layer is added above the image.

    In the diagram, the container's read-write layer is created by making
    a snapshot of the top layer of the image (Layer 1) and creating a clone from
    that snapshot.

4.  As the container modifies the contents of its writable layer, space is
    allocated for the blocks that are changed. By default, these blocks are
    128k.


## How container reads and writes work with `zfs`

### Reading files

Each container's writable layer is a ZFS clone which shares all its data with
the dataset it was created from (the snapshots of its parent layers). Read
operations are fast, even if the data being read is from a deep layer.
This diagram illustrates how block sharing works:

![ZFS block sharing](/Users/baehyunsol/Documents/Rust/ragit/sample/docker/content/manuals/engine/storage/drivers/images/zpool_blocks.webp?w=450)


### Writing files

**Writing a new file**: space is allocated on demand from the underlying `zpool`
and the blocks are written directly into the container's writable layer.

**Modifying an existing file**: space is allocated only for the changed blocks,
and those blocks are written into the container's writable layer using a
copy-on-write (CoW) strategy. This minimizes the size of the layer and increases
write performance.

**Deleting a file or directory**:
  - When you delete a file or directory that exists in a lower layer, the ZFS
    driver masks the existence of the file or directory in the container's
    writable layer, even though the file or directory still exists in the lower
Title: ZFS Container Operations: Reads, Writes, and Deletes
Summary
This section explains how container reads and writes operate using the ZFS storage driver. Reads are fast due to data sharing with parent layer snapshots. Writing a new file allocates space on demand. Modifying a file uses a copy-on-write strategy, allocating space only for changed blocks. Deleting a file in a lower layer masks its existence in the container's writable layer, while the actual file remains in the lower layer.