Q

Counterpoint: What's so great about block-level access?

This Content Component encountered an error
In articles analyzing the pros and cons of NAS vs. SAN, the issue of file-level vs. block-level access often comes up. In particular, it's often said that databases operate "at the block-level". What is unique about the way a database accesses information that makes block-level access desirable? In a SAN environment, can a client request/receive individual pieces of the database (select blocks) rather than the entire database? I'm not certain where the efficiencies come in.
The issue is really one of buffering. Typically file systems or virtual memory managers cache data in the processor memory in order to improve performance. Since they don't know anything about the application that is running, they use some generalized best efforts. The application (in this case the database) knows more about the data access and can be written to do its own buffering (or caching if you like). To do that, the file system caching must be bypassed. This requires what is termed "raw I/O" by the database where it will directly do the block I/O to the device ( LUN). There have been great improvements in file systems such that is not as significant an issue as it used to be.

Read Greg Schulz' answer to this question.

This was first published in August 2004

Dig deeper on SAN management

Pro+

Features

Enjoy the benefits of Pro+ membership, learn more and join.

Have a question for an expert?

Please add a title for your question

Get answers from a TechTarget expert on whatever's puzzling you.

You will be able to add details on the next page.

0 comments

Oldest 

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to:

-ADS BY GOOGLE

SearchSolidStateStorage

SearchVirtualStorage

SearchCloudStorage

SearchDisasterRecovery

SearchDataBackup

Close