Linked by Thom Holwerda on Fri 8th Jul 2005 21:11 UTC
Sun Solaris, OpenSolaris Some key features that Sun was touting last year for the Solaris 10 platform are still missing in action. The two most important are the Project Janus Linux runtime environment and the ZFS file system. While there has been much speculation that Sun will withdraw support for Project Janus, this is not the case.
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by evert on Sat 9th Jul 2005 08:17 UTC
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ZFS indeed looks cool, both for enterprise and desktop usage. personally i like the measures they have taken to protect the data. From the Sun website:

Provable data integrity
ZFS protects all data with 64-bit checksums that detect and correct silent data corruption.

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 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.

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