Re: What is a Block Device?

Hi !

Well, the difference between a block and a raw(or character) device is that a block device uses OS buffer cache and is more specific to physical devices that work with blocks (like disks). Raw devices bypass any kind of buffer. If you go to /dev and list the pseudofiles with "ls -l | more", you'll find a "c" before raw devices and a"b" before block devices. At first, it would have a better performance because of the caching effect. And if the bock size is big, you'll feel the "spatial locality" working. That is, in one read, you will bring along more data that is physically close to that you originally wanted. And according to statistics, this other data will very likely be used in the near future. Its maintenace difficulties are the same.

Chakravarthy KM Nalamotu escreveu na mensagem <83e1ja$au0$1_at_news.hawaii.edu>...
>Hello Oracle Users,
>According to Oracle8 tuning manual a block device gives
>better performance than a raw device and a UNIX file
>system when large block sizes are used.
>I know what a raw device is and what a UNIX file system is.
>What is a Block Device? How does it work? Does it have
>maintenance difficulties similar to raw device?
>Thank you for your responses.
> Kittu.
>
Received on Sat Dec 18 1999 - 13:10:15 CST