RAID array-level selection

We usually have a RAID array level choice when deploying servers, and RAID technology has grown to dozens of today, but we often use only a few of our production systems, such as 0,1,5,0+1. Reader friends may be familiar with the various levels of RAID theory and can even recite it, but there may not be much psychological when it comes to choosing the raid level that is best suited to the application system in a production system, this article gives an introduction to the Oracle database server when selecting a RAID array level. Hope to reassure people who still have doubts.

First, take a look at the pros and cons of several common raid levels.

RAID level	pros and cons description
No raid	Any raid has a certain administrative overhead, if you most need data write speed, and do not need to protect the data, then you can choose not to use RAID, if you have 3 hard drives, you can use one of the installation of operating system and database software, the second block used to store data files, The third block is used for storing log files, so the overall performance of the system will be very good, but any hard drive is broken, the system maintenance time is longer, of course, if you have more hard disk, that can be the work of each hard disk to further refine, such as special take a piece of storage control files and parameter files, but also can be multiple Data file separate, each file a hard disk, so performance can only say is greatly good.
RAID0	People who are familiar with RAID 0 know that it has the highest read and write speed, because the data is divided into small pieces, across multiple hard disk synchronization to write multiple hard drives, so write speed is very fast, if you do not believe that you can make three hard drives into RAID 0, and then install the operating system, you will find that the installation time reduced a lot. Of course, the speed of reading data is significantly higher than a single hard drive, but there are not many people in this raid, because once one of the hard drives is broken, data recovery may have to be a professional recovery company. RAID 0 is ideal for caching as a proxy server, with speed.
RAID1	The purpose of RAID 1 design is to ensure data security, usually we call it mirroring, that is, if you make two hard drives into RAID 1, then the size of the hard disk you see in the operating system is only one size, and the other one is mirrored, so in this case, a single piece of data is saved in two, Allowed to break one piece without affecting the operating system and the normal use of the application, but its disadvantage is that the write speed is less than a single hard disk, after all, write two times to write, will certainly consume a certain amount of CPU time slices. This raid is ideal for applications that value data security, such as unit finance software.
Raid0+1	As can be seen from its name, this is a combination of RAID 0 and RAID 1 technology that leverages RAID 0 's high-speed features and RAID 1 mirroring capabilities to meet the needs of users with the same emphasis on speed and data security. To implement this raid, you need at least 4 hard drives to allow one of the hard drives to break down without affecting the operating system and applications. Particularly suitable for both large data needs access, while the data security requirements of the areas such as banking, finance, etc.
RAID 5	RAID 5 can be understood as a compromise between RAID 0 and RAID 1, with RAID 5 having the same data read speed as RAID 0, but one more parity information, which is slower to write data than to write to a single disk. At the same time, because multiple data correspond to parity information, RAID 5 has a higher disk space utilization ratio than RAID 1 and has a relatively low storage cost. To implement this raid, you need at least 3 hard drives to allow one of the hard drives to break down without affecting the operating system and applications.

In the case of a server that is ready to install Oracle, what kind of RAID is appropriate, and I want to tell you that there is no conclusion that in order to make your Oracle Server final performance is ideal, here is a possible way to summarize.

Start by planning which disks hold what files, then look at the read and write performance requirements of these files, and then do the corresponding RAID level array according to the performance requirements. The following are the types of files involved in Oracle and the RAID levels we recommend, and explain the reasons for the recommendation: <!--. STYLE1 {color: #FFFFFF; font-weight:bold;}-->

File type	Recommended RAID levels	Recommended reasons
Control file	No raid RAID 0 RAID 0+1	I recommend 3 RAID levels to store the control files. Because the control files are constantly updated, the faster the better. However, you need to be careful when using RAID 0 or not using RAID storage control files, to do a good job of backup, there is a point to be aware of the best use of multiple control files, a bad, and perhaps several others are good, so that you can directly use a good control file coverage of the damaged to recover.
Redo Online Log files	No raid RAID 0 RAID 0+1	Like control files, online redo log file updates are also very frequent and must be considered with fast RAID levels. Note that it is recommended that you use more than one online redo log file.
Temporary data File	No raid RAID 0	Temporary files focus on fast access, do not care about how reliable it is, if the data file is lost can be quickly rebuilt in situ. So here I recommend using RAID 0 or not using RAID.
Archive log File	No raid RAID 0 RAID 0+1	The archive process can consume a lot of system resources while archiving the log, so the quicker the better, if you use RAID 0 or do not use RAID, it is recommended to make several copies, and if you are using RAID 0+1, you can rest easy.
Rollback/Undo Data files	RAID 0+1	These files require constant I/O, and the data needs to be protected because Oracle cannot provide multiple copies of it, as in the case of control files, to take the form of hardware to provide more protection, so I recommend a raid 0+1
Data files	RAID 5 RAID 0+1	Most of the I/O operations for data files are in the cache, the physical write operation is done in the background, so RAID 5 can reduce costs without impacting performance, recommend it, and if the I/O operation is very frequent and RAID 5 already feels slow, raid 0+1.

Some people may see there will be doubt, according to this design, how many hard drive ah, yes, to reduce maintenance time, enhance data security, to ensure the application performance, it does require a lot of hard drives to form different forms of raid. If you still have questions, here are some of the principles you can consider in space planning:

If you have enough budget, you can use RAID 0+1 to separate storage for all Oracle files.
To reduce costs, you can put data files on a RAID 5 array.
If you want to reduce the cost, you can put all your data files on a RAID 5 array.
If not, you can put the archive log file and rollback/redo table space on a RAID 5 array.
Finally, you can only store all files using a raid 5来.