e35088c93f
A problem with zio_flush() is that it issues a flush ZIO to a top-level vdev, which then recursively issues child flush ZIOs until the real leaf devices are flushed. As usual, an error in a child ZIO results in the parent ZIO erroring too, so if a leaf device has failed, it's flush ZIO will fail, and so will the entire flush operation. This didn't matter when we used to ignore flush errors, but now that we propagate them, the flush error propagates into the ZIL write ZIO. This causes the ZIL to believe its write failed, and fall back to a full txg wait. This still provides correct behaviour for zil_commit() callers (eg fsync()) but it ruins performance. We cannot simply skip flushing failed vdevs, because the associated write may have succeeded before the vdev failed, which would give the appearance the write is fully flushed when it is not. Neither can we issue a "syncing write" to the device (eg SCSI FUA), as this also degrades performance. The answer is that we must bind writes and flushes together in a way such that we only flush the physical devices that we wrote to. This adds a "vdev tracing" facility to ZIOs, zio_vdev_trace. When enabled on a ZIO with ZIO_FLAG_VDEV_TRACE, then upon successful completion (in the _done handler), zio->io_vdev_trace_tree will have a list of zio_vdev_trace_t objects that each describe a vdev that was involved in the successful completion of the ZIO. A companion function, zio_vdev_trace_flush(), is included, that issues a flush ZIO to the child vdevs on the given trace tree. zil_lwb_write_done() is updated to use this to bind ZIL writes and flushes together. The tracing facility is similar in many ways to the "deferred flushing" facility inside the ZIL, to the point where it can replace it. Now, if the flush should be deferred, the trace records from the writing ZIO are captured and combined with any captured from previous writes. When its finally time to issue the flush, we issue it to the entire accumulated set of traced vdevs. Sponsored-by: Klara, Inc. Sponsored-by: Wasabi Technology, Inc. Signed-off-by: Rob Norris <rob.norris@klarasystems.com> |
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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 any supported branches and releases starting from 13.0-RELEASE.