Re: A database on raw devices. How to get back to file system based?

On 27 Aug 2001 20:41:19 -0500, Galen Boyer <galenboyer_at_hotpop.com> wrote:

>back to UNIX. Does Oracle need to release anything ..., or can I
>shutdown the instance and then have the sysadmin just reconfigure
>the disk drives to be file based. Then, go about my business of
>creating a new database?

Pretty much so. Shutdown the old stuff, tell the sys admin to reuse the raw devices for a file system, and bingo. You will *definitely* loose the data that was there vefore, unless you can export it somewhere else before the raw devices go.

>
>I'm worried that the executables might get munged in this process
>and I'm worried about whatever else this group might deem that I
>should worry about :-)

I can't see how that can happen, unless your sys admin gets over-enthusiastic! ORACLE executables have to be stored in a file system, they cannot be inside a raw device. That means unless your sys admin dismounts the file system where they live and reformats it, there is no way loosing the raw devices should affect them.

>
>I'm guessing it is as easy as having the sysadmin just
>reinitialize the disks and then my just recreating a new
>database, and not having to worry at all, but raw isn't something
>that I have ever worked with.
>

It's actually quite simple, Galen. A raw device is the basic "partitioning" of a disk in UNIX. Think of it as the UNIX equivalent of "fdisk" in PCs (not exactly, but similar enough for this purpose). It basically represents a "chunk" of disk that the OS recognizes as contiguous, unformatted disk space.

This "chunk" or "raw device" can be used by itself (like ORACLE can do for storing data), in which case UNIX simply sends the I/O commands directly to the disk and doesn't care about keeping track of directories, files, free space, used space, etc. ORACLE does that.

It can also be assigned as the disk area to be used to implement a "mount point" in UNIX. Ie, it can be "added" to an existing file system (to give it more space) or be itself the disk space for a new file system.

In this case, UNIX now manages the used and free space in that raw device, as well as how to get at the files using things like bitmap block maps, directories, etc. The end result of which is what you see in UNIX if you type the "ls -l" command.

There are all sorts of add-ons that can be used with raw devices such as LVMs (logical volume managers). These use the raw "partitions" to build up virtual drives, RAID arrangements, etc,etc.

But at the core and assuming basic use, a raw device is just an unformatted disk partition.
HTH Cheers
Nuno Souto
nsouto_at_optushome.com.au.nospam Received on Tue Aug 28 2001 - 05:41:26 CDT