As I understand it, with windoze systems, when you modify a file, you completely rewrite it as a new file. Those blocks that belonged to the "old" file are maintained in the snapshot inode listing. This is not an issue with Unix (As I understand it). So with file folding, the contents of the active file system are compared against the most recent snapshot (only) to determine if blocks are duplicates and can be freed. Also, small files (less than 64K, which really are written to the inode) NT streams and directories are not folded.
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-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com]On Behalf Of Timothy Cook Sent: Thursday, December 12, 2002 3:47 PM To: toasters@mathworks.com Subject: Re: file folding impact
As I understand it, with windoze systems, when you modify a file, you completely rewrite it as a new file. Those blocks that belonged to the "old" file are maintained in the snapshot inode listing. This is not an issue with Unix (As I understand it). So with file folding, the contents of the active file system are compared against the most recent snapshot (only) to determine if blocks are duplicates and can be freed. Also, small files (less than 64K, which really are written to the inode) NT streams and directories are not folded.
It must be dependent on the application doing the writing. We are primarily using our filer to hold Domino databases. Many of these are over half a gig. They definitely get changed all the time, and if it were rewriting the entire file, it seems like we would be using much more snapshot than we are, not to mention the time it would take to rewrite the entire file.
Jordan
-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com]On Behalf Of Timothy Cook Sent: Thursday, December 12, 2002 3:47 PM To: toasters@mathworks.com Subject: Re: file folding impact
As I understand it, with windoze systems, when you modify a file, you completely rewrite it as a new file. Those blocks that belonged to the "old" file are maintained in the snapshot inode listing. This is not an issue with Unix (As I understand it). So with file folding, the contents of the active file system are compared against the most recent snapshot (only) to determine if blocks are duplicates and can be freed. Also, small files (less than 64K, which really are written to the inode) NT streams and directories are not folded.
It must be dependent on the application doing the writing. We are primarily using our filer to hold Domino databases. Many of these are over half a gig. They definitely get changed all the time, and if it were rewriting the entire file, it seems like we would be using much more snapshot than we are, not to mention the time it would take to rewrite the entire file.
Very true. Database applications tend to update individual file blocks rather than rewrite the entire file. File folding isn't necessary.
For file folding to be useful, your application must
1) rewrite the original file rather than update blocks "in place".
2) the original file and the new file must have blocks with identical data so that they can be folded.
Steve Losen scl@virginia.edu phone: 434-924-0640
University of Virginia ITC Unix Support
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Jordan Share -
Steve Losen -
Timothy Cook