Posts Tagged by SQL

The RAID5 Write Hole

14-Jan-2011 Posted by Sonia Hamilton under , ,
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The latest edition of the venerable UNIX and Linux System Administration Handbook (Nemeth et al) has a good section discussing the “RAID5 Write Hole”:

Finally, RAID 5 is vulnerable to corruption in certain circumstances. Its incremental updating of parity data is more efficient than reading the entire stripe and recalculating the stripe’s parity based on the original data. On the other hand, it means that at no point is parity data ever validated or recalculated. If any block in a stripe should fall out of sync with the parity block, that fact will never become evident in normal use; reads of the data blocks will still return the correct data.

Only when a disk fails does the problem become apparent. The parity block will likely have been rewritten many times since the occurrence of the original desynchronization. Therefore, the reconstructed data block on the replacement disk will consist of essentially random data.

Further reading on the BAARF archive (Battle Against Any Raid 5), including why RAID10 and RAID3 should be chosen over RAID5. And then there’s ZFS and RAID-Z.

MSSQL Resources

13-Jun-2007 Posted by Sonia Hamilton under , , ,
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Web Sites

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MSSQL 2005 AdventureWorks Schemas

24-May-2007 Posted by Sonia Hamilton under ,
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Here are schema diagrams for the Microsoft SQL 2005 AdventureWorks sample database:

sql 2000 administration exercise

09-Nov-2005 Posted by Sonia Hamilton under , ,
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Scenario

A complete install of a Microsoft Sql 2000 Server instance, and the creation of some additional objects.

Members

Work in groups of three. One member of each team will be nominated as the TEAM LEADER who will co-ordinate job responsibilities with the rest of the group. (more…)