CentOS 7

Your local metadata seems to be corrupted.Try:

yum clean all
rm -rf /var/cache/yum

And then installing zabbix again.

This is a brand new install. Nothing else has been done other than

yum check-update

yum update

and that is it. nothing has been done yet on this system.

Extra fresh CentOS 7 install.

Here is the full unhappy message

yum -y install zabbix-server-mysql zabbix-web-mysql zabbix-agent
Loaded plugins: fastestmirror, langpacks
Determining fastest mirrors

• base: mirror.csclub.uwaterloo.ca
• extras: mirror.csclub.uwaterloo.ca
• updates: mirror.netflash.net
  base | 3.6 kB 00:00:00
  extras | 3.4 kB 00:00:00
  updates | 3.4 kB 00:00:00
  zabbix | 2.9 kB 00:00:00
  zabbix-non-supported | 951 B 00:00:00
  (1/5): updates/7/x86_64/primary_db | 2.4 MB 00:00:00
  (2/5): base/7/x86_64/group_gz | 166 kB 00:00:00
  (3/5): extras/7/x86_64/primary_db | 180 kB 00:00:00
  (4/5): base/7/x86_64/primary_db | 6.0 MB 00:00:00
  zabbix/x86_64/primary_db FAILED
  http://repo.zabbix.com/zabbix/4.0/rhel/7/x86_64/repodata/6842e98407e78c66b975f98432ba9422077e0646292de0c24fbff625d56b6421-primary.sqlite.bz2: [Errno -1] Metadat a file does not match checksum
  Trying other mirror.
  zabbix-non-supported/x86_64/pr FAILED
  http://repo.zabbix.com/non-supported/rhel/7/x86_64/repodata/primary.xml.gz: [Errno -1] Metadata file does not match checksum 0.0 B/s | 0 B 00:00:00
  Trying other mirror.
  zabbix/x86_64/primary_db FAILED
  http://repo.zabbix.com/zabbix/4.0/rhel/7/x86_64/repodata/6842e98407e78c66b975f98432ba9422077e0646292de0c24fbff625d56b6421-primary.sqlite.bz2: [Errno -1] Metadat a file does not match checksum
  Trying other mirror.
  zabbix/x86_64/primary_db | 5.4 kB 00:00:00
  http://repo.zabbix.com/zabbix/4.0/rhel/7/x86_64/repodata/6842e98407e78c66b975f98432ba9422077e0646292de0c24fbff625d56b6421-primary.sqlite.bz2: [Errno -1] Metadat a file does not match checksum
  Trying other mirror.

One of the configured repositories failed (Zabbix Official Repository - x86_64),
and yum doesn't have enough cached data to continue. At this point the only
safe thing yum can do is fail. There are a few ways to work "fix" this:

1. Contact the upstream for the repository and get them to fix the problem.

2. Reconfigure the baseurl/etc. for the repository, to point to a working
upstream. This is most often useful if you are using a newer
distribution release than is supported by the repository (and the
packages for the previous distribution release still work).

3. Run the command with the repository temporarily disabled
yum --disablerepo=zabbix ...

4. Disable the repository permanently, so yum won't use it by default. Yum
will then just ignore the repository until you permanently enable it
again or use --enablerepo for temporary usage:

yum-config-manager --disable zabbix
or
subscription-manager repos --disable=zabbix

5. Configure the failing repository to be skipped, if it is unavailable.
Note that yum will try to contact the repo. when it runs most commands,
so will have to try and fail each time (and thus. yum will be be much
slower). If it is a very temporary problem though, this is often a nice
compromise:

yum-config-manager --save --setopt=zabbix.skip_if_unavailable=true

failure: repodata/6842e98407e78c66b975f98432ba9422077e0646292de0c24fbff625d56b6421-primary.sqlite.bz2 from zabbix: [Errno 256] No more mirrors to try.
http://repo.zabbix.com/zabbix/4.0/rhel/7/x86_64/repodata/6842e98407e78c66b975f98432ba9422077e0646292de0c24fbff625d56b6421-primary.sqlite.bz2: [Errno -1] Metadat a file does not match checksum

nm, CentOS sucks

The upstream is fine, we few people have just checked it. I suggest removing your yum cache directory

rm -rf /var/cache/yum

Another thing, make sure you have enough disk space where your /var is mounted.