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100 lines
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ReStructuredText
100 lines
4.8 KiB
ReStructuredText
..
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Normally, there are no heading levels assigned to certain characters as the structure is
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determined from the succession of headings. However, this convention is used in Python’s
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Style Guide for documenting which you may follow:
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# with overline, for parts
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* for chapters
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= for sections
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- for subsections
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^ for subsubsections
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" for paragraphs
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########################
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Tuning Backup Parameters
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########################
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Restic offers a few parameters that allow tuning the backup. The default values should
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work well in general although specific use cases can benefit from different non-default
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values. As the restic commands evolve over time, the optimal value for each parameter
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can also change across restic versions.
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Disabling Backup Progress Estimation
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====================================
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When you start a backup, restic will concurrently count the number of files and
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their total size, which is used to estimate how long it will take. This will
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cause some extra I/O, which can slow down backups of network file systems or
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FUSE mounts. To avoid this overhead at the cost of not seeing a progress
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estimate, use the ``--no-scan`` option which disables this file scanning.
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Backend Connections
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===================
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Restic uses a global limit for the number of concurrent connections to a backend.
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This limit can be configured using ``-o <backend-name>.connections=5``, for example for
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the REST backend the parameter would be ``-o rest.connections=5``. By default restic uses
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``5`` connections for each backend, except for the local backend which uses a limit of ``2``.
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The defaults should work well in most cases. For high-latency backends it can be beneficial
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to increase the number of connections. Please be aware that this increases the resource
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consumption of restic and that a too high connection count *will degrade performance*.
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CPU Usage
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=========
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By default, restic uses all available CPU cores. You can set the environment variable
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`GOMAXPROCS` to limit the number of used CPU cores. For example to use a single CPU core,
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use `GOMAXPROCS=1`. Limiting the number of usable CPU cores, can slightly reduce the memory
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usage of restic.
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Compression
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===========
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For a repository using at least repository format version 2, you can configure how data
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is compressed with the option ``--compression``. It can be set to ``auto`` (the default,
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which will compress very fast), ``max`` (which will trade backup speed and CPU usage for
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slightly better compression), or ``off`` (which disables compression). Each setting is
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only applied for the single run of restic. The option can also be set via the environment
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variable ``RESTIC_COMPRESSION``.
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File Read Concurrency
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=====================
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When backing up files from fast storage like NVMe disks, it can be beneficial to increase
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the read concurrency. This can increase the overall performance of the backup operation
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by reading more files in parallel. You can specify the concurrency of file reads with the
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``RESTIC_READ_CONCURRENCY`` environment variable or the ``--read-concurrency`` option of
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the ``backup`` command.
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Pack Size
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=========
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In certain instances, such as very large repositories (in the TiB range) or very fast
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upload connections, it is desirable to use larger pack sizes to reduce the number of
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files in the repository and improve upload performance. Notable examples are OpenStack
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Swift and some Google Drive Team accounts, where there are hard limits on the total
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number of files. Larger pack sizes can also improve the backup speed for a repository
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stored on a local HDD. This can be achieved by either using the ``--pack-size`` option
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or defining the ``$RESTIC_PACK_SIZE`` environment variable. Restic currently defaults
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to a 16 MiB pack size.
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The side effect of increasing the pack size is requiring more disk space for temporary pack
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files created before uploading. The space must be available in the system default temp
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directory, unless overwritten by setting the ``$TMPDIR`` environment variable. In addition,
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depending on the backend the memory usage can also increase by a similar amount. Restic
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requires temporary space according to the pack size, multiplied by the number
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of backend connections plus one. For example, if the backend uses 5 connections (the default
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for most backends), with a target pack size of 64 MiB, you'll need a *minimum* of 384 MiB
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of space in the temp directory. A bit of tuning may be required to strike a balance between
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resource usage at the backup client and the number of pack files in the repository.
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Note that larger pack files increase the chance that the temporary pack files are written
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to disk. An operating system usually caches file write operations in memory and writes
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them to disk after a short delay. As larger pack files take longer to upload, this
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increases the chance of these files being written to disk. This can increase disk wear
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for SSDs.
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