Installation guide

Cluster Hardware Consideraons for Oracle RAC
This secon covers some of the issues that you should consider when choosing hardware for your Oracle RAC system. Two of the key
issues are how to choose the right RAID level for your shared storage, and how to choose the right amount of memory for your RAC
servers.
RAID Systems
Managing a large number of individual disk drives can be very dicult, since you must balance the database les across all of these
disk drives in order to spread out the I/O load. In order to simplify this task, provide for opmal performance and to provide a fault
tolerant system, RAID systems were developed. RAID stands for Redundant Array of Inexpensive Disks.
RAID systems are very congurable, depending on what your needs are. These dierent conguraons have dierent performance
and fault tolerant properes and are known as RAID levels. These RAID levels work dierently but essenally serve the same
purpose, to create a logical disk drive out of two or more physical disks. A logical disk drive orlogical volume looks to the operang
system and relaonal database management system (RDBMS) like a disk drive, but in reality might be the combinaon of many disk
drives. RAID volumes are combinaons of mulple disk drives congured in a RAID array to provide the desired performance and
fault tolerant properes.
RAID 0
RAID 0 is considered a RAID level even though there are no redundant properes associated with this RAID level. A RAID 0 takes a
number of disk drives and stripes them into a larger logical volume. By using RAID 0 you can combine or stripe mulple disk drives
into what appears to the operang system as a single large disk drive. RAID 0 works by taking the data in the logical volume and
striping that data across the array. The data in the logical volume is broken down into what are known as chunks or stripes
(depending on the vendor). These chunks are typically 64K, 32K or congurable in size. The chunks are then allocated to the physical
disk drives in a round-robin fashion.
In an RDBMS environment, it is not recommended to use RAID 0. In the event of a disk failure (and disk failures are probably the
most likely type of failure to occur) all of the data or programs would be lost and you must recover from backup.
RAID 1 and RAID 10
RAID 1 is known as mirroring. With RAID 1 the enre contents of your disk drive has an exact copy on another disk drive, known as
the mirror. With RAID 1 a disk drive failure is transparent to the user. If a disk drive were to fail, the mirrored disk drive immediately
takes over. The term fault tolerance refers to the fact that the system can tolerate a fault, such as the loss of a disk drive and connue
processing seamlessly.
RAID 10 or RAID 0+1 is a combinaon of RAID 0 and RAID 1. With a RAID 10 conguraon disk drives are mirrored and then striped.
Thus you can take advantage of the RAID 0 disk volume where you can increase space and performance as well as taking advantage
of the mirroring properes of RAID 1.