[CentOS-mirror] Rsync command line (hard links)

[Anssi Johansson]

Cochrane, Bryan T kirjoitti 22.6.2018 klo 14.46:
> rsync -ah --stats --delete eu-msync.centos.org::CentOS /bak/centos/CentOS

I believe you can sync OK now, but a comment on this command line.

rsync's -h option is "output numbers in a human-readable format". While 
that may be nice for logging purposes and such, I would recommend adding 
the -H option as well. -H is "preserve hard links", which is 
particularly useful at point release times.

For a slightly simplified example, 6.9's rpms take up around 8 GB of 
disk space. The updated packages in the upcoming 6.10 take up around 1 
GB. If your rsync does not use that -H option, you will need to download 
around 8 GB of 6.10 packages when 6.10 gets released. If you have -H 
enabled, you will need to download only that 1 GB of fresh 6.10 
packages. The remaining unchanged packages (around 7 GB) will be hard 
linked between 6.9 and 6.10, and transferring this hard link information 
is very quick.

Each hard linked file needs to be stored on disk only once, saving you 
some hard disk space.

If you (or any others reading this message) don't have -H in your rsync 
command line, please add it. The next time you sync your mirror, rsync 
will remove the duplicate files and create hard links for them.

In certain rare situations the underlying file system does not 
understand hard links. In this case the -H flag won't help.