RE: Question on Gaja's Raid Document

Because a single datafile may be striped across 16 disks. In the case of 16 datafiles on 16 disks, Oracle knows that they are separate files, but it is down to you to set the degree of parallelism, because Oracle can't know about your underlying physical configuration. With a stripe set, a single data file is likely to span all disks, therefore all heads would be used in when Oracle wants to read a lot of blocks sequentially. The only scope for acceleration on such a configuration would be for the RAID drivers to make the OS reads underlying the Oracle reads faster, effectively getting filesystem blocks in parallel (rather than Oracle blocks) and passing them on.

g

-----Original Message-----
Sent: Thursday, September 20, 2001 3:20 PM To: Multiple recipients of list ORACLE-L

List,

While reading Gaja's excellent document on Implementing Raid on Oracle Systems, Gaja mentions the following in his document.

"The degree of striping in the DATA and INDX volumes should also consider
factors such as data/index partitioning, availability requirements and support for parallel operations. Please note that 16 datafiles placed on 16
individual drives can support a 16-way parallel operation (if you have memory and CPU to support it and your controller is not out of capacity because all 16 drives engaged at the same time). The same cannot be concluded with 16 datafiles placed on a 16-way RAID volume with 16 drives.
The degree of parallelism that you deploy on a 16-way volume will be significantly less, when compared to the former configuration of 16 individual drives. This factor should be factored, when making "degree of
striping" decisions, which in turn controls the number of volumes on your
system. "

Question:

Why the degree of parallelism is less on a 16-way volume compared to 16 individual drives?

Thanks,

Rao

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Rao, Maheswara
  INET: Maheswara.Rao_at_Sungardp3.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L


(or the name of mailing list you want to be removed from).  You may

also send the HELP command for other information (like subscribing).
--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Guy Hammond
  INET: guy.hammond_at_avt.co.uk

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L


(or the name of mailing list you want to be removed from).  You may

also send the HELP command for other information (like subscribing).