ZFS Internal Structure
By Deirdre' Straughan on Apr 26, 2010
This talk explains the basic elements of the ZFS filesystem and the corresponding structures in the on-disk format. ZFS belongs to a new generation of filesystems, which are able to keep up with the pace of the developing disk subsystems and new challenges in data processing. But how does it work?
Transactions are implemented with COW; the talk explains which data structures from uberblock over the internal tree to the leaf nodes on the disk are modified during that. Some applications like databases emit a high number of synchronous writes which have to be implemented differently; ZFS keeps the integrity with the ZFS Intent Log.
The tasks of the Data Management Unit (DMU) and the Storage Pool Allocator (SPA) are explained and why ZFS is able to optimize better than traditional filesystems. The structures mantained by DMU and SPA are examined. Directories and other mappings are implemented with ZAP (ZFS Attribute Processor) and variants (micro-ZAP). It is explained how it works and where it is used. Free space in ZFS is mantained with regard to the blocks still in use by snapshots. The talk explains how this works over multiple disks. ZFS can use SSDs in the critical areas for faster log writing (aka LOGZILLA) and for fast access to frequently read data (aka READZILLA). ZFS caching algorithm ARC implements this.
A presentation at OSDEVCON 2009 by Ulrich Gräf:
TH Darmstadt (now TU Darmstadt) 1985 - 1991:
- Graduation in Computer Science (Diplom-Informatiker) Darmstadt)
- System Programming Group - Assistant for Computer Science base lectures
- Implementing mail services on base of EARN for BS2000 and PCS (Unix)
- HRZ (university computing center) implementing the services for the Internet connection of TH Darmstadt.
- Sun Microsystems Inc: (1992 - )
- Systems Engineer for financial services (banks, insurances, partners)
- Benchmarking Engineer for customer application benchmarks
- Platform Technology Team - Systems Engineer and OS Ambassador
- Evangelizing new technologies to customers
- Big projects
- Enabling customers, partners
- Technology presentations for customers, partners, communities
NOTE, 2014: We lost Uli last year, so we are especially pleased to be able to bring back this video as at least one way to honor his contributions.
Learn more: Oracle Solaris ZFS Technology at the Oracle Technology Network