Oracle-L: Raid 0+1 or Raid 1+0

From: <George.Leonard_at_za.didata.com>
Date: Thu, 22 May 2003 00:06:53 -0800
Message-ID: <F001.0059F7FA.20030522000653@fatcity.com>

Hi all

Some documents I read says use RAID 0 + 1 but then if you look at what happens when a single drive fails you switch over to the other side of the raid, thus you can only tolerate 1 drive failure before a second drive failure brings the storage system down,

Raid 0 + 1 = Stripe + Mirror which equates to Oracle SAME methodology

Whereas

Using Raid 1 + 0 gives the same performance but you can handle multiple drive failures.

Views and comments please.

George

George Leonard
Oracle Database Administrator
Dimension Data (Pty) Ltd
(Reg. No. 1987/006597/07)
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-----Original Message-----
Sent: 22 May 2003 08:32 AM
To: Multiple recipients of list ORACLE-L

Hi all
here is a question

Q. You need to determine the amount of space currently used in each tablespace.
You can retrieve this information in a single SQL statment using only one DBA view in the FROM clause providing you use either the _______ or _______ DBA view.

A.DBA_EXTENTS. B.DBA_SEGMENTS. C.DBA_DATA_FILES. D.DBA_TABLESPACES. I was thinking that dba_extents and dba_segments would be the correct answer because i could use :
select tablespace_name, sum(bytes) from dba_extents group by tablespace_name ;

select tablespace_name, sum(bytes) from dba_segments group by tablespace_name;

But The answer given says dba_extents and dba_data_files. Is the given answer wrong or is there some way of finding out from dba_data_files how much space is used up in a tablespace

For that matter what does the question want to know ? does it want to know how much space do the tablespaces have ( that would be the sum of the sizes of the data files ) or how much is ""used up"" ?

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