Re: Data Mirroring on two data centers -- How to use ASM ?
- From: "Alex Gorbachev" <gorbyx@xxxxxxxxx>
- To: adar666@xxxxxxxxxxxx, db.mail.1@xxxxxxxxx
- Date: Fri, 19 May 2006 18:25:50 +0200
Can you please clarify why you need the second set in the second data
center.
I believe this is to mitigate the risk of loosing a data center. Kind
of disaster recovery site. The requirement doesn't say that RAC
instances must be in different data centers so they can run in one
location.
In fact, the requirement is either interpreted wrong or stated wrong
(proposing EXACT solution instead of requesting SOME solution). Better
solution using Oracle tools for remote datacenter replication would be
physical standby. Alternatives, as Adar mentioned using third party
replication.
1) You have one RAC node in each center, so each node will access the
local copy.
This is not possible with ASM as there is no concept of "local" disks
and remote disks. In ASM there is a concept of primary extent and
secondary extent. ASM will try to distribute all primary extents
equally across all disks in a diskgroup. Write is done to both places
and read is always done from primary extent (unless it's unavailable).
Assuming that your data is quite well distributed (which is the case
with ASM) _AND_ all your disks deliver equal performance, this is a
good approach.
The latter "_and_" actially makes it quite a risk to put one of
failure groups to remote datacenter as half of read operations will go
to remote SAN box.
Dynamic rebalancing for performance is NOT implemeted in ASM as some
might be confused. It seems this confusion is quite common - automatic
rebalancing in ASM is based purely on assumption that all data must be
distributed as equal as possible and it doesn't take into
consideration different performance characteristics of disks/SAN
boxes.
> Hello All,
>
> We are planning on testing a two node 10g RAC using ASM for one of our
> database on pSeries using AIX 5.3. We have a primary requirement of
> mirroring data across TWO data centers (Hitachi SAN).
--
Best regards,
Alex Gorbachev
http://oracloid.blogspot.com
--
//www.freelists.org/webpage/oracle-l
Other related posts:
