One or multiple virtual disks?
Yesterday I read an article form Carlo Costanzo from VMwareInfo.com about the need for multiple disks in a virtualized environment. This is a discussion much like the physical/virtual vCenter issue. When you create a virtual machine do you need to create multiple virtual disks or do you create one large virtual disk. When you ask five people you will probably get five different opinions. Personally I like to create two virtual disks when I create a standard virtual machine, one for the operating system and applications like Exchange and SQL, and one for all temporary files like page file and install files. The first one is 10GB and the second one 5GB by default.
Why this setup? There is no performance gain. I like to keep things organized and like the possibility to modify disk size independently of each other. I know a system disk size can be modified but when I enlarge a systems memory size and want to modify the page file accordingly I don’t want the hassle and just want to increase the size of my second volume.
This is all without any data disks, this is pure operating system, application and page file. What about data volumes?
When you do need a data volume for Exchange or SQL databases and logs I would recommend using an extra virtual disk as you can place these virtual disks on LUNs with different RAID/performance levels to match your virtual disk needs accordingly. For instance, databases on LUNs with RAID level 5 and logs on LUNs with RAID level 1.
So when creating a serious Exchange back end server I create the following (virtual) disks:
- Operating system – virtual disk
- Temporary files (page file) – virtual disk
- Exchange databases – virtual disk or RDM (depending on the size) (vRAID 5)
- Exchange logs – virtual disk or RDM (depending on the size) (vRAID 1)
- Exchange queues (MTA, SMTP) – virtual disk (vRAID 1)
It’s a whole lot of disks but in this senario you will know exactly where everything is located, performance and redundancy is not an issue as every disk has the performance and redundancy level it requires and the volumes have no direct impact on each other.