From the SUSE page:

Delta RPM packages contain the difference between an old and a new version of an RPM package. Applying a delta RPM on an old RPM results in the complete new RPM. It is not necessary to have a copy of the old RPM, because a delta RPM can also work with an installed RPM. The delta RPM packages are even smaller in size than patch RPMs, which is an advantage when transferring update packages over the Internet. The drawback is that update operations with delta RPMs involved consume considerably more CPU cycles than plain or patch RPMs.

Delta rpms disabled because usr bin applydeltarpm not installed red hat or centos

1. Open the terminal application. For remote CentOS / Red Hat (RHEL) server use ssh for login
2. Type sudo yum install deltarpm to enable deltarpm support
3. Test your installation by running sudo yum update command
4. Verify that “Delta RPMs disabled because applydeltarpm not installed” warnings went away

Let us see all commands and procedure in details to get started with delta rpms.

Delta RPMs disabled because /usr/bin/applydeltarpm not installed

Let us try to update the system:
$ sudo yum update

Get started with delta rpms on a CentOS / Red Hat (RHEL)

Search for deltarpm package, run the following yum command:
yum search deltarpm
yum info deltarpm
Sample outputs:

Loaded plugins: copr
Available Packages
Name        : deltarpm
Arch        : x86_64
Version     : 3.6
Release     : 3.el7
Size        : 82 k
Repo        : base/7/x86_64
Summary     : Create deltas between rpms
URL         : http://gitorious.org/deltarpm/deltarpm
License     : BSD
Description : A deltarpm contains the difference between an old
            : and a new version of a rpm, which makes it possible
            : to recreate the new rpm from the deltarpm and the old
            : one. You don't have to have a copy of the old rpm,
            : deltarpms can also work with installed rpms.

Installation

Simply run the following command:
sudo yum install deltarpm

Test it

Again, run:
sudo yum update

Conclusion

You learned about delta rpms (DRMS) that can save bandwidth and speed up download patches and rpm packages from the Internet.