Preparing for Exadata - Oracle Exadata Recipes: A Problem-Solution Approach - page 149

4 MB AU size, the first 4 MB of data for a newly created segment will be placed on the first disk in the disk group, the
second 4 MB will be stored on the second disk, the third 4 MB on the third disk, and so forth. In other words, the ASM
AU size can be viewed as the stripe size.
When physical I/O is performed on the Exadata storage cells, cellsrv reads and writes in units of a storage
region . These storage regions are 1 MB in size, and you can confirm this by tracing the cellsrv process or running the
following MegaCli64 command:
[root@cm01cel01 ~]# /opt/MegaRAID/MegaCli/MegaCli64 -LDInfo -Lall -aALL | grep Stripe
Stripe Size : 1.0 MB
Knowing that I/O is conducted in units of the 1 MB storage region implies that I/O for database extents with
smaller sizes will still perform 1 MB reads and writes regardless of a potentially smaller extent size. Thus, unless you
can guarantee that nearly all your I/O will be buffered I/O satisfied via database buffer cache logical reads, there is no
benefit in configuring smaller extent sizes and, in fact, it could be detrimental from a performance perspective.
6-8. Completing the Pre-Delivery Survey
Problem
You're the proud owner of a brand new Exadata Database Machine and would like some guidance filling out Exadata's
pre-delivery survey. Specifically, you would like to know which parts of the pre-delivery survey are the most important
to enter correctly to ensure a smooth, delay-free installation.
Solution
After you place your Exadata Database Machine order, Oracle or your Oracle Partner will send a pre-delivery survey
that you must fill out. The pre-delivery spreadsheet is a simple Excel spreadsheet containing a number of delivery
logistics questions.
Filling out the pre-delivery survey should be relatively straightforward. In our experience, the most important
consideration is to ensure you enter information accurately in the power-related sections. This governs which power
distribution units are shipped with your Exadata rack. If you happen to provide the incorrect power specifications, it
can lead to delays and either a potentially costly data center power circuit change or complicated PDU change order
process. The Exadata PDUs are available in single-phase low voltage, single-phase high voltage, three-phase low
voltage, and three-phase high voltage. You should select the power option that matches the power circuit capabilities
in your data center. Additionally, an important point to consider is the location of your power plugs (above rack or
under the floor).
In addition to the power specifications, there are a few other aspects of the pre-delivery survey to take note of.
Look closely at the physical dimensions in the Exadata pre-delivery survey under the Internal Delivery Questions
section and validate that you have enough floor space to support your new Exadata rack.
In addition to validating the weight requirements and physical dimensions of your doors, elevators, and hallways,
pay special attention to the floor footprint requirements (23.6" x 47.2"). Data centers may have unique floor tile
arrangements and structures so it is important to have precise tile measurements to ensure the Exadata rack will fit
nicely on your data center floor.
One data center detail not covered in the pre-delivery survey is the topic of interconnected Exadata machines.
The InfiniBand switch cables are 50' in length, so your racks should be less than 50', plus any additional distance
required to accommodate any top-rack or below-rack cabling distances. You can, at additional cost, elect to purchase
100' InfiniBand cables, but this can be expensive.