Database Reference
In-Depth Information
raID OVerVIeW
While a full discussion of RAid and how it is used is beyond the scope of this topic, here are some useful
facts to help you understand the basics:
•
RAid is a collection of two or more hard drives that are made to look like a single
hard drive.
•
Your software, such as sQl server, does not know there are multiple hard drives
involved.
•
A stripe places some parts of your data on one drive and other parts on a different
hard drive. if one of the drives fails, you have only part of your data!
•
A mirror keeps a real-time copy of your data. if a drive fails, you still have the copy.
•
RAid 0 uses only striping. Although this is faster than using a single hard drive, your
data could be at risk. Therefore, make sure you back up your important files regularly.
•
RAid 1 uses mirroring. Essentially this means your data has a real-time backup at all
times. it will not, however, keep track of historical changes to data. Earlier versions
of updated files become lost if you do not create and store regular backups of your
important files.
•
RAid 0 is faster than RAid 1 when it comes to writing data to the drives, since RAid
1 has to write twice as much. Read performance is similar, though.
•
RAid 1 is limited to two hard drives, but RAid 0 is not. The more drives you add to
the array, the faster the performance.
•
RAid 1+0 combines both mirroring and striping to give you the best of both worlds!
You are not restricted to only two drives; in fact, you need at least four to start with,
and it includes the real-time copy of your data.
if you are interested in learning more about this subject, we recommend searching the internet for “RAid.”
One common scenario is to place your data source on a RAID 1+0 array that provides mirroring fault
tolerance, as well as additional performance, for both transactional and query statements. In a RAID 1+0 array,
your database is spread across two or more hard drives, and a mirror of the database is also spread across two or
Figure 18-5.
A database on a RAID 1+0 array of hard drives
