Re: Oracle-managed RAID-like tablespaces

Rick Denoire <100.17706_at_germanynet.de> wrote in message news:<u2l8kugq70nghp8m6elnkesomuv7gh1gbs_at_4ax.com>...
>
> If I understand you correctly, a LVM would allow me to setup a kind of
> "logical device" that is based across several "real" harddisks, and
> that accessing this logical device from within an application would
> lead to a multiple access of several disks.

Precisely. Not only that, but you can also get different kinds of logical devices. Simple example: assume 2 disks. You can partition each in two and end up with four surfaces. Now, you can say RAID-0 two of them and RAID-1 the other two.

And any other combination and permutations you can think of. Then, you can assign each one of these to either a "raw device" or a file system, which in turn can be used as a datafile in a tablespace.

> fine feature. I suppose that I could also choose the size of the data
> chunks written as a unit to every disks before switching to the next
> disk (inside the same "logical device").

Yes, it's called the "interleave factor" in some of them, in others it's the "stripe factor". Used mostly with RAID-0. But is also used with other levels of RAID that implicitly include striping.

>
> Can I do this without any hardware *Raid* controller? Please confirm.

Absolutely! To the best of my knowledge.

> Of course, you are right here. But according to Mr. Sven Jensen in
> this thread one can achieve the mentioned organisation of data by
> putting several files which build a locally managed tablespace on
> different disks, and Oracle would address different files in a round
> robin order, in this way spreading data over several disks that would
> otherwise be written sequentially into one file.

Yes, but it's not flexible. Suppose you later on want to change that "round-robbin" block factor? You gotta unload the TS, redo volumes and reload it again. With a LVM and RAID-0 (striping), you don't have to unload any data. Just save the volume, redo the logical partition and copy back. Done.

Cheers
Nuno Souto
nsouto_at_optushome.com.au Received on Mon Jul 29 2002 - 00:47:44 CDT