From: Greg Willits <lists@...>
Date: 2009-07-06T16:44:35+09:00
Subject: Re: file.seek and unused bytes

Brian Candler wrote:
> Greg Willits wrote:
>> I still don't see where the nulls come from (if they're not being 
>> written)
> 
> All disk I/O is done in terms of whole blocks (typically 1K)
> 
> Whenever the filesystem adds a new block to a file, insteading of 
> reading the existing contents into the VFS cache it just zero-fills a 
> block in the VFS cache. A write to an offset then updates that block and 
> marks it 'dirty'. The entire block will then at some point get written 
> back to disk, including of course any of the zeros which were not 
> overwritten with user data.

Ah. That's what I was looking for. thanks.
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