Zfs architecture

ZFS architecture: a layered approach to data storage and management
ZFS, which stands for Zettabyte File System, is an advanced file system and logical volume manager renowned for its robust data integrity, impressive scalability, and simplified administration. Unlike traditional file systems that separate volume management from file system functionality, ZFS integrates both into a unified system, offering a range of powerful features like pooling, snapshots, cloning, data deduplication, and checksumming. 
Here's a breakdown of the key components of ZFS:
1. Storage pools
The foundation of ZFS is the storage pool, which is a collection of physical or virtual devices (vdevs) that are combined to create a single pool of storage space.
From these pools, you can create and manage various datasets, which can be either mountable file systems or block devices. 
2. Virtual devices (vdevs)
Vdevs organize the disks within a ZFS pool in a hierarchical tree structure.
At the top is the root vdev, and its children are known as top-level vdevs.
These top-level vdevs can be:
Mirrors: Two or more disks mirrored for redundancy (RAID 1).
RAID-Z: Provides striping with parity, similar to RAID-5 or RAID-6, allowing for data recovery even with disk failures.
RAID-Z1 allows for one disk failure.
RAID-Z2 allows for two disk failures.
RAID-Z3 allows for three disk failures.
Single Disks or Files: Used as individual storage units. (Using files as vdevs is not recommended for production environments due to potential layering issues).
Special Vdev Types: In addition to standard storage vdevs, ZFS also supports:
Log devices (SLOG): Store ZFS Intent Log records to accelerate synchronous writes, particularly beneficial with fast storage like SSDs.
Cache devices (L2ARC): Used to extend ZFS's in-memory cache (ARC) by utilizing fast storage devices (SSDs) to cache frequently accessed data, thereby reducing the need for disk I/O operations.
Spare devices: Act as hot spares, automatically replacing a failed drive in a redundant pool if the autoreplace property is enabled. 
3. Datasets
Datasets are the basic unit of storage resource allocation within a ZFS pool.
They are like independent file systems within a pool and can be used for:
Storing files (like a traditional file system).
Creating volumes (zvols), which are block devices.
Taking snapshots and clones. 
4. Copy-on-Write (CoW) mechanism
ZFS utilizes a Copy-on-Write (CoW) transactional model. When data is modified, ZFS writes the new data to a different block instead of overwriting the original, preserving the old data until the new data is successfully written. This helps prevent data loss from issues like power failures. 
5. Snapshots and clones
Snapshots are read-only copies of a file system or volume at a specific point in time. Due to the CoW mechanism, they are created quickly and initially use minimal space. Snapshots are useful for backups and recovery. Clones are writable copies of snapshots. They share data with the original snapshot, but changes to a clone are stored separately. Clones are valuable for testing or creating temporary copies. 
6. Data integrity and self-healing
ZFS uses checksums for every data block to verify data integrity. If corruption is detected, ZFS can automatically repair the data using redundant copies in mirrored or RAID-Z configurations. The zpool scrub command can also be used to check for and repair corruption proactively. 
This overview highlights the key architectural components of ZFS, illustrating its robust features for managing and protecting data effectively