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The motivation for upgrading our PRNG is the recent buildbot failures in the ZTS' tests/functional/fault/decompress_fault test. The probability of a failure in that test is 0.8^256, which is ~1.6e-25 out of 1, yet we have observed multiple test failures in it. This suggests a problem with our random number generation. The xorshift128+ generator that we were using has been replaced by newer generators that have "better statistical properties". After doing some reading, it turns out that these generators have "low linear complexity of the lowest bits", which could explain the ZTS test failures. We do two things to try to fix this: 1. We upgrade from xorshift128+ to xoshiro256++ 1.0. 2. We tweak random_get_pseudo_bytes() to copy the higher order bytes first. It is hoped that this will fix the test failures in tests/functional/fault/decompress_fault, although I have not done simulations. I am skeptical that any simulations I do on a PRNG with a period of 2^256 - 1 would be meaningful. Since we have raised the minimum kernel version to 3.10 since this was first implemented, we have the option of using the Linux kernel's get_random_int(). However, I am not currently prepared to do performance tests to ensure that this would not be a regression (for the time being), so we opt for upgrading our PRNG to a newer one from Sebastiano Vigna. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de> Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu> Closes #13983 |
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OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.
Official Resources
- Documentation - for using and developing this repo
- ZoL Site - Linux release info & links
- Mailing lists
- OpenZFS site - for conference videos and info on other platforms (illumos, OSX, Windows, etc)
Installation
Full documentation for installing OpenZFS on your favorite operating system can be found at the Getting Started Page.
Contribute & Develop
We have a separate document with contribution guidelines.
We have a Code of Conduct.
Release
OpenZFS is released under a CDDL license.
For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197
Supported Kernels
- The
METAfile contains the officially recognized supported Linux kernel versions. - Supported FreeBSD versions are any supported branches and releases starting from 12.2-RELEASE.