RE: Oracle Parallel Server / Other HA Solutions

Hmmm... Isn't OPS an HA solution? ...But like everything else, it needs to be properly implemented. Most OPS installations are on RAID1+0 so you should be protected from a disk failure but you're not protected from a catastrophic failure of the entire RAID cabinet. There's a difference between planning for high availability and disaster recovery. What are you looking to achieve with your architecture? High availability or disaster recovery? Or both? There are differences and there is no one solution to meet the needs of both. If you are looking for BOTH then you may need to consider integrating 2 or 3 solutions as part of your overall architecture. How about if you need to patch/recompile Oracle but keep the database available?

If you're looking at high availability then OPS should be considered. However, OPS does not prepare you for a disaster since the clustered machines are usually in the same data center. If there is a "site failure" then the only means to rebuild your infrastructure is to recreate it on new machines from backup tapes and this means lots of down time. To address this some Oracle shops implement both OPS and a standby database. OPS addresses the high availability needs and the standby database addresses the disaster recovery needs.

To recover every committed transaction with a standby database you not only need to apply the archived logs but you may need to get copies of the "current" redo logs from the primary database. What are the chances that your entire data center will be obliterated and you cannot recover one of the mirrored copies of the redo logs? If you want to protect yourself from this remote possibility then be prepared to pay big bucks for some kind of "geographic disk mirroring" solution. (Like EMC's SRDF.) But if you're going to go through the expense of geographic disk mirroring then you may as well mirror more than just the redo logs. I understand that fiber channel can be separated by about 60 kilometers and maybe in the future there will be less expensive
ways for IT shops to implement this without having to buy huge, expensive 3rd party "boxed" solutions.

Replication is generally asynchronous and it may require a considerable development effort to make it fault proof and hot failover capable. You may need to consider this very carefully before taking this on.

On Metalink there's a white paper "Failover Options in Oracle8" by Erik Peterson. It's kind of dated and doesn't take into account some the enhancements of Oracle8i. There's a paper from Lawrence To on the "Oracle8i Standby Database" and of course there's lots of Oracle sales propaganda on the Oracle8i high availability enhancements but I believe the complete, seminal work on how to architect all the Oracle HA features has yet to be written. :-(

IMHO,
Steve Orr

-----Original Message-----
From: root_at_fatcity.com [mailto:root_at_fatcity.com]On Behalf Of Jared Still Sent: Thursday, October 12, 2000 11:00 AM To: Multiple recipients of list ORACLE-L Subject: Re: Oracle Parallel Server / Other HA Solutions

Mary,

OPS is not an HA solution. While you may still have an instance running if a node goes down, the storage medium is still a single point of failure.

Jared

On Thu, 12 Oct 2000, Ruiz, Mary A (CAP, CDI) wrote:

> I need a little advice. We have a fairly new (< 1 year) 8.1.5 instance
to
> support my company's internet business. We recently changed our network
> solutions provider and now my management wants to achieve a higher level
of
> redundancy than it currently does with mirrored disks. The solution being
> proposed by my Sysadmin is an Oracle Parallel Server solution. Some
> background is in order here - we have always shut our databases down at
> night for backups. I am not highly skilled in backup and recovery
although
> I tried some of the hot backup techniques from this list and was able to
> recover successfully to another server. I noticed that the course offered
> by Oracle in OPS has backup and recovery as well as performance tuning as
> pre-requisites, which indicates to me that OPS could be extremely
> challenging. Also, I have read mainly unfavorable comments about OPS from
> this list, but most of those comments were based on the Oracle 7
> implementations (High administrative costs, difficult to implement, etc.).
>
> Have things improved with Oracle 8i ? Is OPS worth pursuing? Or should I
> convince my management that extra $$ spent in, say, a hot standby database
> is well worth it? Is there any other solution that would not involve a
> second set of disks, rather a second database on the same set of disks ??
>
> Thanks in advance,
> Mary Ruiz / Atlanta
>
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> Author: Ruiz, Mary A (CAP, CDI)
> INET: Mary.Ruiz_at_gecapital.com
>
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Jared Still
Certified Oracle DBA and Part Time Perl Evangelist ;-) Regence BlueCross BlueShield of Oregon
jkstill_at_bcbso.com - Work - preferred address jkstill_at_teleport.com - private

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Author: Jared Still
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