Hi,
I'm having problems understanding some terminologies recently.
1. Marice bach, page 328, (The Design of Unix OS) says 'fsck should not be run on an active filesystem bacause it does raw I/O.' What do you mean by 'active'. And what would be it if it were not active?
2. Raw I/O bypasses the filesystem. So, suppose I have a database management program that does raw I/O on its records so that it can dictate the exact disk blocks in which it wants to put the data. How do I know which blocks are free if I bypass the filesystem servies? And, later if the filesystem is creating a new file, how does it know whether the block on its free list is actually free and not occupied by any record that is being maintained by my DBMS program through raw I/O.

Pardon me if I'm really asking something stupid. And correct me too.

An active filesystem refers to a filesystem that has activity on it, whether it be writing data to files or executing individual programs. When you run fsck, you want to run it in single user mode so you don't have a mass of tasks running in the background.

The database, in your example, would keep track of such things in a manner similar to the vmm managing your swap space. In order to do this, you need to creare a raw partition, which is basically a partition without a filesystem on it, again, like your swap space. Whereas the swap is managed by the VMM, the raw disk space is managed by the dbm. Although this method of database storage offers the most speed for disk access, compared to going through a file system, the negative side of this is that the only way to see it is through the utilities supplied by the dbm. Since the dbm is managing that partition, none of the normal system commands, such as ls, cd, cp, cpio, tar, etc. would work on it.

Hope this helps some. -mk

I get the impression from your answer that all DBMS that manage records through raw I/O have to have another raw partition instead with being the regular filesyste.
I think Oracle does raw I/O. That's why you can never see where the data is stored on your disk whithout the use of Oracle itself. I think apart from spped, it also adds to security. But Oracle can be loaded with regular filesystems on the same partition. So, how can my question be answered in this light.

Thanks.