Quiz

The Oracle Guru Answer #4

The Oracle Guru Were you correct? This week's answer is:
e. RAID 5

According to SearchOracle.com expert Brian Peasland: "RAID 5 is similar to RAID 3, where parity bits are computed and used to reconstruct lost data. The difference is that the parity bits are not stored on a separate disk, they are striped across all disk interspersed with the data.

"RAID 5's biggest advantage is that it uses the least amount of disk space for recovering lost data. So you don't have to buy as much disk. Unfortunately, RAID 5 has the worst write performance of all of these RAID levels. Write operations can be twice as slow compared to a normal file system. No write intensive files should be placed on RAID 5 volumes, otherwise your database peroformance can really slow to a crawl. People like RAID 5 because it is the cheapest solution -- but the write penalties make this RAID level unacceptable for most Oracle databases, in my opinion.

"That being said, I do have one multiterabyte database that uses RAID 5 for most operations. This database gets updated once every two months. So the database writes are kept to a minimum. The database is "read-mostly." But any write intensive database files for this database (online redo logs, control files, etc.) are placed on RAID 0+1 volumes."

Click for the full glossary definition.

For more information:

Expert response: Performance costs with RAID vs. non-RAID

Expert response: Databases on RAID 5 devices

Expert response: Databases on RAID 5 devices, part two

White paper: Implementing RAID on Oracle Systems

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This was first published in August 2003

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