a3a4b8def7
Investigating influence of scrub (especially sequential) on random read latency I've noticed that on some HDDs single 4KB read may take up to 4 seconds! Deeper investigation shown that many HDDs heavily prioritize sequential reads even when those are submitted with queue depth of 1. This patch addresses the latency from two sides: - by using _min_active queue depths for non-interactive requests while the interactive request(s) are active and few requests after; - by throttling it further if no interactive requests has completed while configured amount of non-interactive did. While there, I've also modified vdev_queue_class_to_issue() to give more chances to schedule at least _min_active requests to the lowest priorities. It should reduce starvation if several non-interactive processes are running same time with some interactive and I think should make possible setting of zfs_vdev_max_active to as low as 1. I've benchmarked this change with 4KB random reads from ZVOL with 16KB block size on newly written non-fragmented pool. On fragmented pool I also saw improvements, but not so dramatic. Below are log2 histograms of the random read latency in milliseconds for different devices: 4 2x mirror vdevs of SATA HDD WDC WD20EFRX-68EUZN0 before: 0, 0, 2, 1, 12, 21, 19, 18, 10, 15, 17, 21 after: 0, 0, 0, 24, 101, 195, 419, 250, 47, 4, 0, 0 , that means maximum latency reduction from 2s to 500ms. 4 2x mirror vdevs of SATA HDD WDC WD80EFZX-68UW8N0 before: 0, 0, 2, 31, 38, 28, 18, 12, 17, 20, 24, 10, 3 after: 0, 0, 55, 247, 455, 470, 412, 181, 36, 0, 0, 0, 0 , i.e. from 4s to 250ms. 1 SAS HDD SEAGATE ST14000NM0048 before: 0, 0, 29, 70, 107, 45, 27, 1, 0, 0, 1, 4, 19 after: 1, 29, 681, 1261, 676, 1633, 67, 1, 0, 0, 0, 0, 0 , i.e. from 4s to 125ms. 1 SAS SSD SEAGATE XS3840TE70014 before (microseconds): 0, 0, 0, 0, 0, 0, 0, 0, 70, 18343, 82548, 618 after: 0, 0, 0, 0, 0, 0, 0, 0, 283, 92351, 34844, 90 I've also measured scrub time during the test and on idle pools. On idle fragmented pool I've measured scrub getting few percent faster due to use of QD3 instead of QD2 before. On idle non-fragmented pool I've measured no difference. On busy non-fragmented pool I've measured scrub time increase about 1.5-1.7x, while IOPS increase reached 5-9x. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Matthew Ahrens <mahrens@delphix.com> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored-By: iXsystems, Inc. Closes #11166 |
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README.md
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 12-STABLE and 13-CURRENT.