One of the first and most obvious concessions a DBA makes in a virtualized server world is that there is yet another layer of hardware and software abstraction being forced into the overall equation. That latest injection of virtualization is pervasive now throughout all the hardware and software levels. The entire technology stack is very quickly becoming less and less concrete in day to day terms. Gone are the good old days of being able to walk into a server room and point to your hardware. Also gone are the days of sizing totally independent of all other systems (remember, everything’s becoming shared assets). We live in times where we must plan for our minimum resource needs based upon maintaining certain SLA levels, but we no longer have to make the one-to-one correspondence between our needs and a single server. Instead, we need to express those needs clearly enough so that someone can meet those requirements while deploying our database within their asset pool.

But fear not, for DBAs have embraced abstraction for years, even if they have forgotten about this fact. For example, as disk drives became bigger and file systems could support ever larger files, the logical volume manager appeared as an abstraction technique to simplify storage management. So we evolved in our database storage thinking and planning as solutions built upon the foundations shown below by Figure 2.

Figure 2:  Examples of Database Storage

Before Logical Volume Managers (LVMs), we assigned storage space to tablespace data files as either raw disks or cooked files. Of course, one could also argue that the file system was actually the first abstraction. Then came LVMs, and now we can manage space one additional level removed. Add to that disk storage arrays where logical units or LUNs are allocated and assigned, and we have yet another level of abstraction.

Then along came 9i’s Oracle Managed Files (OMF) and 10g’s Automated Storage Management (shown on the next page in Figure 3). Now we had even more levels and types of storage abstraction. Since such abstraction often and generally made the DBA’s life easier, we embraced such new techniques with minimal skepticism. Oracle even claimed at the 11g new features training that I attended in Dallas in 2007 that “SAME or stripe and mirror everything” was more pervasive than ever before and a totally acceptable practice. In fact, they recommended fewer tablespaces and data files, thereby leaving the details buried in the abstraction. I happen to agree. I now separate tablespaces purely due to logical needs, such as different performance characteristics by which to categorize.

Figure 3:  Examples of Storage Abstraction – OMF and ASM

The point is simply that DBAs have been accepting and doing abstraction for years, even if we forgot or failed to realize it. In fact, the adoption of ASM has been optimistically quoted as 65% of new RAC deployments and 25% of new non-RAC databases. I don’t doubt that for a minute since ASM makes space management so much easier.

Plus, with all the abstractions listed above, even more are happening in addition to server virtualization of which the DBA may or may not be aware. For example, with storage virtualization (example shown in Figure 4), I may be assigned some of my disk space on high speed SCSI drives contained in a fiber channel connected SAN array, some space on a 10-gigabit NAS array, and some space on a 10-gigabit connected iSCSI array. Furthermore, the NAS and iSCSI arrays may contain a mixture of high speed SCSI disks, high speed IDE disks, and, even possibly, some slower speed IDE disks. When we as DBAs ask for a few terabytes of disk space, we tend not to need to know the details and performance characteristics of every component in the stack as long as we meet our SLAs.

Figure 4:  Distribution of Virtualized Storage

Therefore, server virtualization is just another in an ongoing series of abstractions being introduced throughout the technology stack. We as DBAs must become accustomed to and embrace virtualization, because the trend is clear – it’s happening all around us.

This is an excerpt from Oracle on VMWare: Expert tips for database virtualization by Rampant TechPress.