9e20465fd1
We've had a trickle of users who accidentally activate the same pool on a VM and host at the same time. Typically the host doesn't do any IO, but the kernel will still rewrite the superblock on shutdown. This leaves the superblock pointing to very out of date btree roots and so we get massive metadata loss. This patch changes thin_repair, and thin_dump --repair. They now hunt for the most recent, undamaged and consistent roots of the device and mapping trees, and use that as the starting point of the repair. |
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|---|---|---|
| autoconf | ||
| base | ||
| bin | ||
| block-cache | ||
| caching | ||
| contrib | ||
| doc | ||
| era | ||
| features | ||
| ft-lib | ||
| functional-tests | ||
| lib | ||
| man8 | ||
| persistent-data | ||
| thin-provisioning | ||
| ui | ||
| unit-tests | ||
| xml_metadata | ||
| .gitignore | ||
| CHANGES | ||
| configure.ac | ||
| COPYING | ||
| get-gmock.sh | ||
| main.cc | ||
| Makefile.in | ||
| mk_release | ||
| README.md | ||
| TODO.org | ||
| VERSION | ||
| version.h.in | ||
Introduction
A suite of tools for manipulating the metadata of the dm-thin, dm-cache and dm-era device-mapper targets.
Requirements
A C++ compiler that supports the c++11 standard (eg, g++). The Boost C++ library. The expat xml parser library (version 1). The libaio library (note this is not the same as the aio library that you get by linking -lrt) make, autoconf etc.
There are more requirements for testing, detailed below.
Building
autoconf
./configure
make
sudo make install
Quick examples
These tools introduce an xml format for the metadata. This is useful for making backups, or allowing scripting languages to generate or manipulate metadata. A Ruby library for this available; thinp_xml.
To convert the binary metadata format that the kernel uses to this xml format use thin_dump.
thin_dump --format xml /dev/mapper/my_thinp_metadata
To convert xml back to the binary form use thin_restore.
thin_restore -i my_xml -o /dev/mapper/my_thinp_metadata
You should periodically check the health of your metadata, much as you fsck a filesystem. Your volume manager (eg, LVM2) should be doing this for you behind the scenes.
thin_check /dev/mapper/my_thinp_metadata
Checking all the mappings can take some time, you can omit this part of the check if you wish.
thin_check --skip-mappings /dev/mapper/my_thinp_metadata
If your metadata has become corrupt for some reason (device failure, user error, kernel bug), thin_check will tell you what the effects of the corruption are (eg, which thin devices are effected, which mappings).
There are two ways to repair metadata. The simplest is via the thin_repair tool.
thin_repair -i /dev/mapper/broken_metadata_dev -o /dev/mapper/new_metadata_dev
This is a non-destructive operation that writes corrected metadata to a new metadata device.
Alternatively you can go via the xml format (perhaps you want to inspect the repaired metadata before restoring).
thin_dump --repair /dev/mapper/my_metadata > repaired.xml
thin_restore -i repaired.xml -o /dev/mapper/my_metadata
Development
Autoconf
If you've got the source from github you'll need to create the configure script with autoconf. I do this by running:
autoreconf
Enable tests
You will need to enable tests when you configure.
./configure --enable-testing
Unit tests
Unit tests are implemented using the google mock framework. This is a source library that you will have to download. A script is provided to do this for you.
./get-gmock.sh
All tests can be run via:
make unit-test
Alternatively you may want to run a subset of the tests:
make unit-tests/unit_tests
unit-tests/unit_tests --gtest_filter=BtreeTests.*
Functional tests
A bunch of high level tests are implemented in the functional-tests directory. These tests are written in Scheme. To run them you'll need to install chezscheme (http://www.scheme.com/). In addition they make use of the thunderchez (https://github.com/ovenpasta/thunderchez) library.
Make sure the tools that you wish to test are in your PATH, and the thunderchez directory is in the CHEZSCHEMELIBDIRS environment variable.
Then,
cd funtional-tests
./run-tests run
Other command are help and list.
The test framework places temporary files under ./test-output/. By default the tests tidy up after themselves, just leaving a log file for each test. You can turn this off by using the --disable-unlink flag if you want all the artifacts left.
Dump Metadata
To dump the metadata of a live thin pool, you must first create a snapshot of the metadata:
$ dmsetup message vg001-mythinpool-tpool 0 reserve_metadata_snap
Extract the metadata:
$ sudo bin/thin_dump -m /dev/mapper/vg001-mythinpool_tmeta
<superblock uuid="" time="1" transaction="2" data_block_size="128"nr_data_blocks="0">
<device dev_id="1" mapped_blocks="1" transaction="0" creation_time="0" snap_time="1">
<single_mapping origin_block="0" data_block="0" time="0"/>
</device>
<device dev_id="2" mapped_blocks="1" transaction="1" creation_time="1" snap_time="1">
<single_mapping origin_block="0" data_block="0" time="0"/>
</device>
</superblock>
Finally, release the root:
$ dmsetup message vg001-mythinpool-tpool 0 release_metadata_snap