The authors should have made the effort to correlate DRAM error rates to the likelihood of in-memory data corruption by file systems. While suggestions for improved RAM error resistance are well taken - after all, most of the world's computers have no ECC memory - this reinforces the need for ECC DRAM in important applications. I hope that ZFS - or something better - arrives on other OS's soon.īut what about the memory fault tests? In this I suspect that ZFS is no worse than legacy file systems and as a clean sheet design may be better. The disk tests are the strong evidence that ZFS delivers on its promise of superior on-disk data integrity. The authors offer suggestions for making ZFS less vulnerable to DRAM errors.
The results for in-memory data corruption weren't as stellar, but ZFS - like every other file system - wasn't designed to handle DRAM errors. The in-memory caching and periodic flushing of metadata on transaction commits help ZFS recover from serious disk corruptions affecting all copies of metadata. ZFS successfully detects all corruptions and recovers from them as long as one correct copy exists.
ZFS has no special tools against RAM errors. Object updates are grouped together and new copies are created for all the modified blocks. ZFS keeps replicas of certain important blocks. The checksums are stored in parent blocks, which enables ZFS to detect silent data corruption. ZFS has several important data integrity features. As regular readers know, memory errors are hundreds to thousands of times higher than thought. They also injected errors into the RAM the file system used. show that more than 400,000 blocks had checksum mis- matches, 8% of which were discovered during RAID reconstruction, creating the possibility of real data loss.īut the study didn't stop there. In a recent study of 1.53 million disk drives over 41 months, Bairavasundaram et al. We choose ZFS for our analysis because it is a modern and important commercial file system with numerous robustness features, including end-to-end checksums, data replication, and transactional updates the result, according to the designers, is “provable data integrity”ĭisk corruption is more common than you think.
we analyze a state-of-the-art file system, Sun Microsystem’s ZFS, by performing fault injection tests representative of realistic disk and memory corruptions. Fault injection is a great technique because you inject as many errors as you want and correlate the file system's response. The UW-M team used fault injection to test ZFS. It offers the first rigorous test of ZFS data integrity. Arpaci-Dusseau of the Computer Sciences Department, University of Wisconsin-Madison. There is more leading edge storage thinking presented here than any other industry event.Ĭase in point: End-to-end Data Integrity for File Systems: A ZFS Case Study by Yupu Zhang, Abhishek Rajimwale, Andrea C. I'm at the USENIX File and Storage Technology FAST conference (see the last couple of StorageMojo posts for more) in Silicon Valley. The open source ZFS from Sun Oracle claims high data integrity - and now that claim has been tested. File systems guard all the data in your computer, but most are based on 20-30 year old architectures that put your data at risk with every I/O.
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