There are four primary categories impacted by the use of Linked Mode vCenter Server systems. The first is that there is a maximum of 10 Linked vCenter Systems permitted. vCenter Server scales very well, so it would be an incredible infrastructure to roll in 10 different vCenter Server systems. This number can be met quicker if the vCenter environments are smaller due to separation by chargeback, development vs. production, or other business functions. There also can be a maximum of 1,000 hosts in Linked Mode, which is not 10 times the standalone vCenter Server limit. The singular vCenter Server has a maximum of 300 hosts running a 64-bit operating system. The other limits related to Linked Mode are powered-on virtual machines (10,000) and registered virtual machines (15,000). The primary situation where these limits can be reached for many environments is a VMware View VDI environment.

The configuration maximums document does not address a limit for roles and permission models that may be set across vCenter Server systems. With the vCenter Server permissions model, administrators can craft creative roles that are applied to vCenter Server systems. The one caution I would make, as in any permissions model, is to follow Active Directory best practices and not create too many nested levels of permission.

The vCenter Configuration Maximums document is one of the most useful documents, and is a critical tool for the VMware certification path. Be sure to check out the vCenter Server section of the configuration maximums document for all Linked Mode related changes.

vCenter Server for Linux really for Oracle

I downloaded the open virtualization format (OVF) appliance and imported it into my VMware ESX host using the VMware Infrastructure Client — and immediately discovered that vCenter Server for Linux will not work with any database other than Oracle. The rest of the limitations are not as big of a concern and are generally as expected for a technology preview, specifically missing functionality within vCenter for Linux itself. But the lack of support for a database that comes as a part of nearly every Linux distribution is a major issue.

This caveat would not be as much of an issue if VMware’s vCenter Server for Linux offered support for PostgreSQL, MySQL, or even sqlite, but requiring expensive closed source Oracle database for a technology preview is extremely limiting and, quite frankly, a decision that suggests that vCenter Server for Linux was not really created for Linux administrators, but instead for an esoteric few people that have already purchased Oracle. Perhaps this is just a ploy to drive away the possible Linux customers? Or is this a ploy by Oracle to tie Linux vCenter to Oracle and hopefully boost Oracle adoption? I do not know, but not providing interfaces to standard Linux databases is not the Linux way.

Testing MySQL

Being the Linux person that I am, I did attempt to get MySQL to work with vCenter Server for Linux. First I had to get open database connectivity (ODBC) to attach to my MySQL database server, which required editing a few files and making the necessary modifications for MySQL support. Once I finished doing that I could connect using ODBC to MySQL, but I still needed a database to make it work.

I then started with the database schema for Microsoft SQL and made some changes to the schema and database views to allow the databases to work with MySQL. Whoever said SQL works everywhere is fooling themselves! After an upgrade to MySQL 5.1 I finally had everything imported. Restarting the VMware vCenter for Linux server and looking at its log files showed the failure. MySQL is not a recognized database, and VMware vCenter for Linux died. This was just a bit surprising to me.

So what are the supported databases? Doing a little research on the daemon itself I discovered that supported databases are Microsoft SQL, Oracle, PostgreSQL, and something called Other. I am not sure what Other is but it is not something standard with Linux. Since PostgreSQL was in the list, I decided to give it a shot.

Testing PostgreSQL

Once more I hooked up ODBC to my PostgreSQL server and then, starting with the Oracle database schema, ported it to PostgreSQL. After several modifications similar in nature to the ones for MySQL, I had a database schema that would load into PostgreSQL. I restarted vCenter for Linux and noticed it would connect, but returned a very strange error related to the tables. After checking a few logs, I realized it had to be something inside vCenter for Linux that caused the problem, not a PostgreSQL issue.  Perhaps it is related to the way PostgreSQL case folds, but my tests show there is nothing we can do within PostgreSQL to make it work with vCenter Server for Linux.

Conclusions

MySQL and PostgreSQL can handle the database creations as well as the port of the stored procedures, but you are limited to UTF-8 characters within all string variables (which would impact Cryllic and Asian users of vCenter for Linux). VCenter for Linux does not accept the use of MySQL, it will flat out deny its use. PostgreSQL does not get denied but it also will not work as a database for vCenter due to other errors. Some people suggest using the free Oracle database which is available, but it has size and other limitations and then I would have to support yet another database in my environment.

I can only surmise that vCenter for Linux is not a reality for the general GNU/Linux environment but only for enterprise administrators, who may never need vCenter for Linux as they have Microsoft Windows database servers already. I wonder about the target audience for this endeavor. I own a SMB and I am required to run one Windows server just for vCenter. Ideally I wouldn’t have to do this, neither would I like to run Oracle as Oracle is a very expensive option for an SMB. VCenter is expensive as well, but buying one expensive license instead of two is a money savings for many an organization

VMware: Please implement either MySQL or PostgreSQL support and let me use the GNU/Linux tools I already use!