[pve-devel] [PATCH v2 docs] add section about backup compression algorithms

[Aaron Lauterer]

With one optional nit inline:

Reviewed-By: Aaron Lauterer <a.lauterer at proxmox.com>

On 5/7/20 4:16 PM, Alwin Antreich wrote:
> as a short description about the different algorithms in use by vzdump.
> 
> Signed-off-by: Alwin Antreich <a.antreich at proxmox.com>
> ---
> v1 -> v2:
>      * incorporate Aaron's suggestions
>        https://pve.proxmox.com/pipermail/pve-devel/2020-May/043481.html
> 
>   vzdump.adoc | 35 ++++++++++++++++++++++++++++++++++-
>   1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/vzdump.adoc b/vzdump.adoc
> index 404ad09..bc1f4a9 100644
> --- a/vzdump.adoc
> +++ b/vzdump.adoc
> @@ -147,6 +147,39 @@ That way it is possible to store several backup in the same
>   directory. The parameter `maxfiles` can be used to specify the
>   maximum number of backups to keep.
>   
> +Backup File Compression
> +-----------------------
> +
> +The backup file can be compressed with one of the following algorithms: `lzo`
> +footnote:[Lempel–Ziv–Oberhumer a lossless data compression algorithm
> +https://en.wikipedia.org/wiki/Lempel-Ziv-Oberhumer], `gzip` footnote:[gzip -
> +based on the DEFLATE algorithm https://en.wikipedia.org/wiki/Gzip] or `zstd`
> +footnote:[Zstandard a lossless data compression algorithm
> +https://en.wikipedia.org/wiki/Zstandard].
> +
> +Currently, Zstandard (zstd) is the fastest of these three algorithms. And
s/And multi-threading/Multi-threading/

 From a reading flow perspective I would avoid the `And`. But well, that 
could just be personal preference. ¯\_(ツ)_/¯

> +multi-threading is another advantage of zstd over lzo and gzip. Lzo and gzip
> +are more widely used and often installed by default.
> +
> +You can install pigz footnote:[pigz - parallel implementation of gzip
> +https://zlib.net/pigz/] as a drop-in replacement for gzip to provide better
> +performance due to multi-threading. For pigz & zstd, the amount of
> +threads/cores can be adjusted. See the
> +xref:vzdump_configuration[configuration options] below.
> +
> +The extension of the backup file name can usually be used to determine which
> +compression algorithm has been used to create the backup.
> +
> +|===
> +|.zst | Zstandard (zstd) compression
> +|.gz or .tgz | gzip compression
> +|.lzo | lzo compression
> +|===
> +
> +If the backup file name doesn't end with one of the above file extensions, then
> +it was not compressed by vzdump.
> +
> +
>   [[vzdump_restore]]
>   Restore
>   -------
> @@ -203,7 +236,7 @@ per configured storage, this can be done with:
>   # pvesm set STORAGEID --bwlimit restore=KIBs
>   ----
>   
> -
> +[[vzdump_configuration]]
>   Configuration
>   -------------
>   
>