Databases Reference
In-Depth Information
Getting ready
Despite the "I" in RAID, we need a minimum of two or three drives, depending on the RAID
level we want to implement.
Every RAID level has different requirements and offers different performance and data
integrity levels. In this recipe, we will illustrate these requirements for each RAID level.
There is a common requirement, that is, the RAID controller; it can be software-based
at the operating system, firmware level, or hardware-based. The latter offers guaranteed
performance and no overhead on the CPU.
How to do it...
The following steps will demonstrate the various RAID levels; you can chose the right RAID
level by considering the following:
1. RAID 0+1 is preferable for your Oracle database installations.
2. RAID 5 has significant write penalty, so don't use it for storing write-intensive data files
(if RAID 0+1 is available), redo log files, archived redo log files, and undo segments.
You can use it for control files and for data files with a moderate write activity.
How it works...
This recipe has only two steps, which are simple tips to choose the right hardware to obtain
better performance. More than a buy list it's a no-buy list:
1. Starting with step 1, in terms of performance the best RAID level for an Oracle
database is RAID 0+1, also known as RAID 10. The drawback of this option is
the cost of the solution, because it is twice the cost of storage due to mirroring.
Additionally, it uses more complex procedures and hardware to manage the striping.
2. In step 2, we warn against RAID 5. There is a significant write penalty when using
this RAID level, so storing frequently-updated data is not a good choice. Also, redo
log files and archived redo logs don't fit well in this environment, because, on OLTP
databases, there is an intense write activity on these files, and also because undo
segments experience heavy load.
There's more...
To understand different RAID levels better, we will cover the differences between the most
common RAID configurations, highlighting performance considerations related to storing
Oracle database files.
