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https://github.com/markusressel/zfs-inplace-rebalancing
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127 lines
7.4 KiB
Markdown
127 lines
7.4 KiB
Markdown
# zfs-inplace-rebalancing
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Simple bash script to rebalance pool data between all mirrors when adding vdevs to a pool.
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[](https://asciinema.org/a/350222)
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## How it works
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This script recursively traverses all the files in a given directory. Each file is copied with a `.rebalance` suffix, retaining all file attributes. The original is then deleted and the *copy* is renamed back to the name of the original file. When copying a file ZFS will spread the data blocks across all vdevs, effectively distributing/rebalancing the data of the original file (more or less) evenly. This allows the pool data to be rebalanced without the need for a separate backup pool/drive.
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Note that this process is not entirely "in-place", since a file has to be fully copied before the original is deleted. The term is used to make it clear that no additional pool (and therefore hardware) is necessary to use this script. However, this also means that you have to have enough space to create a copy of the biggest file in your target directory for it to work.
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At no point in time are both versions of the original file deleted.
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To make sure file attributes, permissions and file content are maintained when copying the original file, all attributes and the file checksum is compared before removing the original file (if not disabled using `--checksum false`).
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Since file attributes are fully retained, it is not possible to verify if an individual file has been rebalanced. However, this script keeps track of rebalanced files by maintaining a "database" file in its working directory called `rebalance_db.txt` (if not disabled using `--passes 0`). This file contains two lines of text for each processed file:
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* One line for the file path
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* and the next line for the current count of rebalance passes
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```text
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/my/example/pool/file1.mkv
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1
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/my/example/pool/file2.mkv
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1
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```
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## Prerequisites
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### Balance Status
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To check the current balance of a pool use:
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```
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> zpool list -v
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NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
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bpool 1.88G 113M 1.76G - - 2% 5% 1.00x ONLINE -
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mirror 1.88G 113M 1.76G - - 2% 5.88% - ONLINE
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ata-Samsung_SSD_860_EVO_500GB_J0NBL-part2 - - - - - - - - ONLINE
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ata-Samsung_SSD_860_EVO_500GB_S4XB-part2 - - - - - - - - ONLINE
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rpool 460G 3.66G 456G - - 0% 0% 1.00x ONLINE -
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mirror 460G 3.66G 456G - - 0% 0.79% - ONLINE
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ata-Samsung_SSD_860_EVO_500GB_S4BB-part3 - - - - - - - - ONLINE
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ata-Samsung_SSD_860_EVO_500GB_S4XB-part3 - - - - - - - - ONLINE
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vol1 9.06T 3.77T 5.29T - - 13% 41% 1.00x ONLINE -
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mirror 3.62T 1.93T 1.70T - - 25% 53.1% - ONLINE
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ata-WDC_WD40EFRX-68N32N0_WD-WCC - - - - - - - - ONLINE
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ata-ST4000VN008-2DR166_ZM4-part2 - - - - - - - - ONLINE
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mirror 3.62T 1.84T 1.78T - - 8% 50.9% - ONLINE
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ata-ST4000VN008-2DR166_ZM4-part2 - - - - - - - - ONLINE
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ata-WDC_WD40EFRX-68N32N0_WD-WCC-part2 - - - - - - - - ONLINE
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mirror 1.81T 484K 1.81T - - 0% 0.00% - ONLINE
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ata-WDC_WD20EARX-00PASB0_WD-WMA-part2 - - - - - - - - ONLINE
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ata-ST2000DM001-1CH164_Z1E-part2 - - - - - - - - ONLINE
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```
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and have a look at difference of the `CAP` value (`SIZE`/`FREE` vs `ALLOC` ratio) between vdevs.
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### No Deduplication
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Due to the working principle of this script, which essentially creates a duplicate file on purpose, deduplication will most definitely prevent it from working as intended. If you use deduplication you probably have to resort to a more expensive rebalancing method that involves additional drives.
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### Data selection
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Due to the working principle of this script, it is crucial that you **only run it on data that is not actively accessed**, since the original file will be deleted.
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## Installation
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Since this is a simple bash script, there is no package. Simply download the script and make it executable:
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```shell
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curl -O https://raw.githubusercontent.com/markusressel/zfs-inplace-rebalancing/master/zfs-inplace-rebalancing.sh
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chmod +x ./zfs-inplace-rebalancing.sh
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```
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Dependencies:
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* `pacman -S bc` - used for percentage calculation
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## Usage
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**ALWAYS HAVE A BACKUP OF YOUR DATA!**
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You can print a help message by running the script without any parameters:
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```
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./zfs-inplace-rebalancing.sh
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```
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### Parameters
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| Name | Description | Default |
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|-----------|-------------|---------|
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| `-c`<br>`--checksum` | Whether to compare attributes and content of the copied file using an **MD5** checksum. Technically this is a redundent check and consumes a lot of resources, so think twice. | `true` |
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| `-p`<br>`--passes` | The maximum number of rebalance passes per file. Setting this to infinity by using a value `<= 0` might improve performance when rebalancing a lot of small files. | `1` |
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### Example
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Make sure to run this script with a user that has rw permission to all of the files in the target directory.
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The easiest way to achieve this is by **running the script as root**.
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```
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sudo su
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./zfs-inplace-rebalancing.sh --checksum true --passes 1 /pool/path/to/rebalance
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```
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### Things to consider
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Although this script **does** have a progress output (files as well as percentage) it might be a good idea to try a small subfolder first, or process your pool folder layout in manually selected badges. This can also limit the damage done, if anything bad happens.
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When aborting the script midway through, be sure to check the last lines of its output. When cancelling before or during the renaming process a ".rebalance" file might be left and you have to rename (or delete) it manually.
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Although the `--passes` parameter can be used to limit the maximum amount of rebalance passes per file, it is only meant to speedup aborted runs. Individual files will **not be process multiple times automatically**. To reach multiple passes you have to run the script on the same target directory multiple times.
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# Contributing
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GitHub is for social coding: if you want to write code, I encourage contributions through pull requests from forks
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of this repository. Create GitHub tickets for bugs and new features and comment on the ones that you are interested in.
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# Attributions
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This script was inspired by [zfs-balancer](https://github.com/programster/zfs-balancer).
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# Disclaimer
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This software is provided "as is" and "as available", without any warranty.
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**ALWAYS HAVE A BACKUP OF YOUR DATA!**
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