Storage Smarts Answer #38: Controller failure

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QUESTION OF THE WEEK:

Disk mirroring provides data protection in the case of disk failure because data is constantly updated to both disks, where each relies upon a common controller. However, there is an inherent problem in disk mirroring. What is it?

a. Drive reliability is eliminating the need for mirroring
b. Access to data is threatened if the controller fails
c. Data can't be mirrored remotely
d. Mirroring can't handle planned outages
e. Data sets can't be kept in synch

Were you correct? This week's answer is:
b. Access to data is threatened if the controller fails

Disk mirroring (also known as RAID-1) is the practice of duplicating data in separate volumes on two hard disks to make storage more fault-tolerant. Mirroring provides data protection in the case of disk failure, because data is constantly updated to both disks. However, since the separate disks rely upon a common controller, access to both copies of data is threatened if the controller fails. Disk duplexing overcomes this problem; the use of redundant controllers enables continued data access as long as one of the controllers continues to function.

For more information:

Mirroring strategies

SD2002: Mirroring still crucial despite disk drive improvements

Disk mirroring - local or remote

Talking failure in disk arrays

Ask W. Curtis Preston your backup and recovery questions.

Do you have an idea for a quiz question topic? Let us know!


This was first published in January 2003

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