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
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
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.