Q

Primer on file and block level access

Question: Would you explain briefly about file level and block level access?

Sure.

Storage devices use block addresses to figure out where data is stored on them. To get something on or off a storage device, you use its block address. People don't use blocks, file systems and databases use them because they are too complicated for mortals.

Block access is access made by a file system or database (if it's not using a file system) for data. Block access has no knowledge of the file or object -- it just moves data in and out of "block containers."

Files are abstractions made by file systems in an attempt to make it easier for mortals to store and retrieve data.

Files are accessed by "semantics" instructions that tell a file system what to do. Data inside files is accessed by byte-ranges within the file (for instance, the first 20 bytes of a file). File access is made when an application or user submits an instruction to a file system to do something with the data in a file. File access specifies the file that is being worked with.

Regards, 

Marc

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This was first published in June 2003

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