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= Problem While examining a customer's system we noticed unreasonable space usage from a few snapshots due to gang blocks. Under some further analysis we discovered that the pool would create gang blocks because all its disks had non-zero write error counts and they'd be skipped for normal metaslab allocations due to the following if-clause in `metaslab_alloc_dva()`: ``` /* * Avoid writing single-copy data to a failing, * non-redundant vdev, unless we've already tried all * other vdevs. */ if ((vd->vdev_stat.vs_write_errors > 0 || vd->vdev_state < VDEV_STATE_HEALTHY) && d == 0 && !try_hard && vd->vdev_children == 0) { metaslab_trace_add(zal, mg, NULL, psize, d, TRACE_VDEV_ERROR, allocator); goto next; } ``` = Proposed Solution Get rid of the predicate in the if-clause that checks the past write errors of the selected vdev. We still try to allocate from HEALTHY vdevs anyway by checking vdev_state so the past write errors doesn't seem to help us (quite the opposite - it can cause issues in long-lived pools like the one from our customer). = Testing I first created a pool with 3 vdevs: ``` $ zpool list -v volpool NAME SIZE ALLOC FREE volpool 22.5G 117M 22.4G xvdb 7.99G 40.2M 7.46G xvdc 7.99G 39.1M 7.46G xvdd 7.99G 37.8M 7.46G ``` And used `zinject` like so with each one of them: ``` $ sudo zinject -d xvdb -e io -T write -f 0.1 volpool ``` And got the vdevs to the following state: ``` $ zpool status volpool pool: volpool state: ONLINE status: One or more devices has experienced an unrecoverable error. ...<cropped>.. action: Determine if the device needs to be replaced, and clear the ...<cropped>.. config: NAME STATE READ WRITE CKSUM volpool ONLINE 0 0 0 xvdb ONLINE 0 1 0 xvdc ONLINE 0 1 0 xvdd ONLINE 0 4 0 ``` I also double-checked their write error counters with sdb: ``` sdb> spa volpool | vdev | member vdev_stat.vs_write_errors (uint64_t)0 # <---- this is the root vdev (uint64_t)2 (uint64_t)1 (uint64_t)1 ``` Then I checked that I the problem was reproduced in my VM as I the gang count was growing in zdb as I was writting more data: ``` $ sudo zdb volpool | grep gang ganged count: 1384 $ sudo zdb volpool | grep gang ganged count: 1393 $ sudo zdb volpool | grep gang ganged count: 1402 $ sudo zdb volpool | grep gang ganged count: 1414 ``` Then I updated my bits with this patch and the gang count stayed the same. Reviewed-by: Mark Maybee <mark.maybee@delphix.com> Reviewed-by: Matthew Ahrens <mahrens@delphix.com> Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu> Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com> Closes #14003 |
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zfs.release.in |
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
META
file contains the officially recognized supported Linux kernel versions. - Supported FreeBSD versions are any supported branches and releases starting from 12.2-RELEASE.