Oracle RAC: Capacity Planning for your RAC

Brief intro

Implementing RAC, or any
clustered solution, requires planning. Many mission critical applications tend
to be very demanding and are often load balanced both at front end (application
servers) and backend (database servers). Let’s try to break it up into several
components such as network, storage, infrastructure etc.

Designing the Infrastructure

This is the mother of all
foundations. You need to select the platforms, Network configurations and Storage
options carefully. I always advise starting small and smart so that you have a
good “scale-out” plan. The tendency to go out and buy the coolest HP EVA 8000
for your RAC might seem like a great idea when the consultant is on board, but
your TCA (Total Cost of Acquisition) will shoot up to the roof. There are many
options to choose from, but we’ll look at the basic options here, assuming that
you have already made some fundamental choices:

  • Storage
    (SAN, NAS, DAS), Redundant HBA (Host Bus Adapters)

  • Network:
    NICs: High Speed Interconnects, Redundant switches, VLANs, NIC Teaming

  • Software/Application
    stack: OS (Windows, Linux, Solaris, AIX,)

  • Hardware
    optimization (CPUs: AMD or Intel, Dual socket, Quad Socket)

Let’s just break it all up
and start with storage.

Storage Planning

In many cases, storage is
already rested on a SAN or NAS. Be sure to have two redundant SAN switches, connected
to separate power units! We recently had a problem with our SAN where the
hosting firm, (the same place where Google has its farm hosted), made the mistake
of hooking our SANs up to the same power supply. LUN distribution should be of
the same size–I recommend a RAID 5 (SAN RAID 5 are allegedly 5 times faster
than a poor man’s RAID 5)–and then distribute them equally across the storage
processors, 2 port HBAs connecting to each node. This way, you protect SPOF on
Storage Processors, HBA, LUN levels. Ensure LUN visibility from all nodes and
the equal sizing ensures optimal I/O throughput expectations. Be sure to avoid
the Inter Switch Link in the SAN switch, by designing the SAN switch

High Speed Internetwork Connects

Make sure that your high speed inter-network connectivity
is supported and that you have separate network cards to support it (you can
also go ahead and have teaming on two NICs for private traffic and two NICS
teamed for the public traffic) but in any case make sure that the following are
taken into account:

  • Oracle Clusterware is going to use it and the messages are all
    small packets.

  • Oracle database: Transfers both large and small blocks across the
    nodes and is the main user for the HSIs

  • Bandwidth: I have normally seen CAT5e cables but lately just
    separate VLANs for private traffic, all assigned their own 1Gbps NICs.

Note that the 10Gbps NICs are
gearing up for the production, and while we will not deviate from our path,
remember that a lot of other standards are emerging in the wake of the
expensive SAN fabrics, such as FCoE (Fibre Channel over Ethernet), AoE (ATA
over ethernet, iSCSI), etc. Getting back to the interconnect traffic across
the nodes; we can take a look at the messages. They can be small messages
(under 256 bytes) from GES and GCS, they cab be cache fusion block messages or
some tuned parallel query for a load intensive DSS tablespace or a DSS RAC
itself (you may adjust the block size to a much higher value, the default block
size is 8K). Therefore, to do the math, you would want to add up the GES+GCS
messages, Parallel Query messages and the Cache Fusion blocks and then divide that
by the bandwidth they consume per second. Normally with a 1Gbps backbone, you
would expect that this might go fine but there’s no harm in checking the
expected values before you start complaining about the performance issues.

Where do I get my figures?
Simple, check out the AWR reports (we will cover that thoroughly when I have my
laptop RAC fully configured on my Dual Core HP laptop) and you will be able to
get the Cache Fusion Blocks (default 8K), Parallel Query message chunks (8K
default) and the GES+GCS messages. After doing the quick math, you will realize
that a typical 1Gbps NIC is sufficient.

Software Planning

We have covered the
installation test-beds in our ongoing installation series and have tried to
comply with a scalable Virtualized RAC infrastructure, which might even come close
to production planning. Choosing an OS is normally done long before you start
with RAC; if it hasn’t been, choose wisely. Choosing the Oracle install
directory, CLUSTER_HOME, ORACLE_HOME, etc. must reside in their own directory.
We checked the mount points and even provided mirroring on separate virtual
disks for OCR, Voting disk and ASM spfile.

Hardware Planning

Network configurations can
be taken care of in the same way. Switches, VLAN and NICs can be load balanced.
This will ensure that your network is also up, should any of those hardware
appliances fail. Then the choice comes to memory and CPUs–with RAC you are
only in the “horizontal scaling” mode so I wouldn’t worry about that. Also,
note that Oracle RAC is and can be a very Virtualization aware application. Having
said this, virtualization on the processor level will provide a greater
performance win should you choose a 4 socket quad core node. Imagine 16 cores
on a simple DL 585 box, OR if you choose a smaller version, such as a DL 385,
you can achieve an 8 core box! Isn’t that amazing? Make sure that you stick to
some basic procurement policies, like the same type of machines and specs. This
not only helps diagnose problems on the hardware level but also helps propagate
the updates in a uniform manner.


Capacity planning and scaling out is more
than sticking a wet finger in the air. You will certainly need a robust and
reliable infrastructure but you should also note that it is the metrics (we
will cover them extensively in our AWR articles) that will help you determine
when and where you can use more capacity. Be it on a node level (advisable) or
on a per machine level (CPU, Memory etc), meaning the individual scaling up of
each machines. Obviously you start looking at the CPU when it is shooting over a
75% range for a length of time, and rely on your instincts to scale out your
infrastructure before a downtime hits you, but keeping the metrics and practicing
on them (a replica of your production in a Virtualized infrastructure for your
test and development) will help you plan and sustain a highly available RAC


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Tarry Singh

Tarry Singh
Tarry Singh
I have been active in several industries since 1991. While working in the maritime industry I have worked for several Fortune 500 firms such as NYK, A.P. Møller-Mærsk Group. I made a career switch, emigrated, learned a new language and moved into the IT industry starting 2000. Since then I have been a Sr. DBA, (Technical) Project Manager, Sr. Consultant, Infrastructure Specialist (Clustering, Load Balancing, Networks, Databases) and (currently) Virtualization/Cloud Computing Expert and Global Sourcing in the IT industry. My deep understanding of multi-cultural issues (having worked across the globe) and international exposure has not only helped me successfully relaunch my career in a new industry but also helped me stay successful in what I do. I believe in "worknets" and "collective or swarm intelligence". As a trainer (technical as well as non-technical) I have trained staff both on national and international level. I am very devoted, perspicacious and hard working.

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