ZFS: the last word in file systems.

ZFS--the last word in file systems.

The breakthrough file system in Solaris 10 delivers virtually unlimited capacity, provable data integrity, and near-zero administration.

Most system administrators take the limitations of current file systems in stride. After all, file systems are what they are: vulnerable to silent data corruption, brutal to manage, and excruciatingly slow.

ZFS, the dynamic new file system in Sun's Solaris 10 Operating System (Solaris OS), will make you forget everything you thought you knew about file systems. ZFS will be available on all Solaris 10 OS-supported platforms, and all existing applications will run with it. Moreover, ZFS complements Sun's storage management portfolio, including the Sun StorEdge QFS software, which is ideal for sharing business data.

"We've rethought everything and rearchitected it," says Jeff Bonwick, Sun distinguished engineer and chief architect of ZFS. "We've thrown away 20 years of old technology that was based on assumptions no longer true today."

ZFS is supported on both SPARC and x86 platforms. More important, ZFS is endian-neutral. You can easily move disks from a SPARC server to an x86 server. Neither architecture pays a byte-swapping tax due to Sun's patent-pending "adaptive endian-ness" technology, which is unique to ZFS. And you don't have to worry about migration. Sun continues to support the UFS file system.

ZFS meets the needs of a file system for everything from desktops to data centers. Designed with the administrator in mind, ZFS is the only self-healing, self-managing general-purpose file system. It offers:

• Simple administration
  ZFS automates and consolidates complicated storage administration concepts, reducing administrative overhead by 80 percent.
• Provable data integrity
  ZFS protects all data with 64-bit checksums that detect and correct silent data corruption.
• Unlimited scalability
  As the world's first 128-bit file system, ZFS offers 16 billion billion times the capacity of 32- or 64-bit systems.
• Blazing performance
  ZFS is based on a transactional object model that removes most of the traditional constraints on the order of issuing I/Os, which results in huge performance gains.

The Solaris 10 OS, the upcoming release of the industry's leading UNIX platform, integrates powerful new capabilities to deliver extreme levels of performance, availability, and security. ZFS in the Solaris 10 OS complements Sun's existing storage management portfolio, including the Sun StorEdge QFS software, which is ideal for accessing business data in a shared environment. In addition to the ZFS file system reviewed in this article, the Solaris 10 OS includes these revolutionary technologies:     N1 Grid Containers technology delivers a breakthrough approach to system virtualization and resource utilization.     DTrace is a comprehensive dynamic tracing framework that concisely answers questions about system behavior.     Solaris 10 also includes technology that enables running a range of Linux applications at near-native speeds.     The Predictive Self-Healing capabilities in the Solaris 10 OS enable Sun systems to accurately predict component failure and fix what's wrong.

ZFS achieves its impressive performance through a number of techniques:

• Dynamic striping across all devices to maximize throughput
• Copy-on-write design makes most disk writes sequential
• Multiple block sizes, automatically chosen to match workload
• Explicit I/O priority with deadline scheduling
• Globally optimal I/O sorting and aggregation
• Multiple independent prefetch streams with automatic length and stride detection
• Unlimited, instantaneous read/write snapshots
• Parallel, constant-time directory operations

Just as it dramatically eases the suffering of system administrators, ZFS offers relief for your company's bottom line. Because ZFS is built on top of virtual storage pools (unlike traditional file systems that require a separate volume manager), creating and deleting file systems is much less complex. Not only does this eliminate the need to pay for volume manager licenses and allow for single support contracts, it lowers administration costs and increases storage utilization.

ZFS appears to applications as a standard POSIX file system--no porting is required. But to administrators, it presents a pooled storage model that eliminates the antique concept of volumes, as well as all of the related partition management, provisioning, and file system sizing problems. Thousands--even millions--of file systems can all draw from ZFS' common storage pool, each one consuming only as much space as it needs. The combined I/O bandwidth of all of the devices in that storage pool is always available to each file system.

Get Into the Pool

With traditional volumes, storage is fragmented and stranded. With ZFS' common storage pool, there are no partitions to manage. The combined I/O bandwidth of all of the devices in a storage pool is always available to each file system.

Delivering Near-Zero Administration

Two of Sun's goals with ZFS were to do away with many complicated storage administration concepts and automate many common administrative chores.

For example, creating a storage pool, growing a pool, or adding or removing a file system can all be done with a single, simple command--instead of the multistep process (format, newfs, edit/etc/vfstab, and so on) found in traditional file systems and volume managers.

Consider this case: To create a pool, to create three file systems, and then to grow the pool--5 logical steps--5 simple ZFS commands are required, as opposed to 28 steps with a traditional file system and volume manager.

Moreover, these commands are all constant-time and complete in just a few seconds. Traditional file systems and volumes often take hours to configure. In the case above, ZFS reduces the time required to complete the tasks from 40 minutes to under 10 seconds.

ZFS' command-line interface drastically simplifies administration. It is task-oriented, letting administrators express the tasks they want to accomplish instead of having to memorize or look up cryptic commands.

"You don't have to worry about the details of what's going on with your disks, your storage, or your file systems," explains Bonwick. "You add disks to your storage pool, file systems consume space automatically as they need it, and administrators don't have to get involved.

"We wanted to design an integrated system from scratch. If you're willing to take on the entire software stack, there's a lot of innovation possible."

Taking the Guesswork Out of Data Integrity

Data can be corrupted in a number of ways, such as a system error or an unexpected power outage, but ZFS removes this fear of the unknown. ZFS prevents data corruption by keeping data self-consistent at all times. All operations are transactional. This not only maintains consistency but also removes almost all of the constraints on I/O order and allows changes to succeed or fail as a whole.

All operations are also copy-on-write. Live data is never overwritten. ZFS writes data to a new block before changing the data pointers and committing the write. Copy-on-write provides several benefits:

• Always-valid on-disk state
• Consistent, reliable backups
• Data rollback to known point in time

"We validate the entire I/O stack, start to finish, no guesswork involved. It's all provable data integrity," says Bonwick.

Administrators will never again have to run laborious recovery procedures, such as fsck, even if the system is shut down in an unclean fashion. In fact, Solaris Kernel engineers Bill Moore and Matt Ahrens have subjected ZFS to more than a million forced, violent crashes in the course of their testing. Not once has ZFS lost data integrity or leaked a single block.

Additionally, ZFS is the only file system that conducts end-to-end 64-bit checksums on all data to prevent silent data corruption. When any data is read, the checksum is verified to ensure that the data that the application wrote is what is returned.

"The cost of doing something like a checksum is no longer prohibitive. Burning a small percentage of the CPU to know that data is intact is a price that administrators would gladly pay," says Moore.

As part of Sun's quest to build truly self-healing systems (see the September 7 Sun.com feature), ZFS can self-heal data in a mirrored or RAID configuration. When one copy is damaged, ZFS detects it via the checksum and uses another copy to repair it.

No competing product can do this. Traditional mirrors can only handle total failure of a device. They don't have checksums, so they have no idea when a device returns bad data. So even though mirrors replicate data, they have no way to take advantage of it. By contrast, the end-to-end checksums in ZFS allow it to find and fix bad blocks--with nineteen nines certainty--automatically.

Creating Immense Capacity

Sun engineers wondered if the 64-bit capabilities of current file systems will continue to suffice over the next 10 to 20 years. Their answer was no. If Moore's Law holds, in 10 to 15 years people will need a 65th bit. As a 128-bit system, ZFS is designed to support more storage, more file systems, more snapshots, more directory entries, and more files than can possibly be created in the foreseeable future.

This scalability also means that storage can be dynamically added to or removed from storage pools without interrupting services, providing new levels of flexibility and availability for globally accessed application services.

To efficiently use all of this capacity, file systems grow and shrink automatically as users add or remove data. Administrators can set quotas to limit space consumption and reservations to guarantee future availability of space. ZFS also provides compression to reduce disk space and I/O bandwidth requirements.

Logically, the next question is if ZFS' 128 bits is enough. According to Bonwick, it has to be. "Populating 128-bit file systems would exceed the quantum limits of earth-based storage. You couldn't fill a 128-bit storage pool without boiling the oceans."