When many disks are involved in a physical database layout

Dear all,

In Ch4 Physical Database Layouts of Kevin Loney's book, an ideal 22-disk model is presented as:

Disk Contents
1 Oracle software
2 SYSTEM tablespace
3 RBS tablespace
4 DATA tablespace
5 INDEXES tablespace
6 TEMP tablespace
7 TOOLS tablespace
8 Online Redo log 1
9 Online Redo log 2
10 Online Redo log 3
11 Control file 1
12 Control file 2
13 Control file 3
14 Application software
15 RBS_2
16 DATA_2
17 INDEXES_2
18 TEMP_[USER]
19 TOOLS_I
20 USERS
21 Archived redo log destination disk
22 Export dump file desination disk

He then tries in successive iterations to reduce the number of disks to 17-disk, 15-disk, 12-disk, 9-disk and 7-disk solutions.

The goals for the disk layout, he defines, are as follows: 1.The database must be recoverable.
2.The online redo log files must be mirrored via the system or the database.

3.The database file I/O weights must be estimated.
4.Contention between DBWR, LGWR, and ARCH must be minimized.
5.Contention between disks for DBWR must be minimized.
6.The performance goals of the system must be defined.
7.The disk hardware options must be known.
8.The disk mirroring architecture must be known.
9.Disks must be dedicated to the database.

I think the author is trying to cover all kinds of situations, if there are less than 7 disks involved, more compromises have to be made, and this model would become less useful. Unfortunately, the current databases we have all reside on only one disk; control files, data files, online redo log files,... everything lives on the same disk. It seems (I might be wrong) that on Windows NT there seldom are more than 5 disks, and when there are, they could be combined into one by RAID. From the practical point of view, I have questions: 1.Do you usually use 7 or more 'dedicated' disks for an Oracle database?
2.Do you prefer the disks to be RAID'ed or not? 3.Do you DBA's get involvied in the matter of server purchase so that hardware spec. are good for the physical layout? 4.The issue of file sizes is not really taken into account in the decisions about which tablespaces should be placed on which disks by the author. He focuses on reducing and balancing the contentions most of the time. This might imply there are a lot of wasted disk space on disks where data are small, and because disks must be dedicated to the database (rule 9), they will not be used to accomodate other files.

Thanks, Dino Received on Sun May 27 2001 - 09:25:21 CDT