Disk Mirroring or Database Mirroring

[Former Member]

Hi,

Of late we are contemplating as to which mirroring technique to use to mirror our SAP system in real time so that we can fall back during crisis.

Can someone suggest the advantages of disk mirroring over database mirroring? Which one is better of the two?

Our requirement is as follows :-

1) To do 3 way mirroring.

2) The second hard disk will have to be updated in real-time.

3) The third hard disk is to be updated with one day delay, which means this hard disk will always hold one day old image so that we can revert to this old image if there is any damages done by any latest transports which cannot be undone easily. We do not want to rely on backup tapes for this because there can be situations where the tapes are faulty and the second reason is tape restoration is very time consuming.

Is our 3rd requirement is possible with disk and database mirroring?

[former_member182307 · Accepted solution]

Hello,

What is the database you plan to use ?

BR,

steve.

[Former Member · Accepted solution]

Hi,

We are using DB400...

[michael_ruth3 · Accepted solution]

Hi,

On DB2/400 use RAID 5 ,don't use RAID 1, which is the same as disk mirroring. I've been around DB2/400 for over 20 years and RAID 5 is the best for these systems. Read up on it !!!

Cheers

[former_member182307]

Hello,

Im' not a specialist over DB2/400 but what you are trying to achieve is closer to database mirroring.

IE : you have a database running on your primary site and the modification are replicated to other sites in which standby databases are replaying the modifications using the database's logs.

Oracle, for example, has a mechanism called dataguard that is able to replay the redo logs of your database to several standby databases.

To answer to your requirements, here is what I would say :

1) To do 3 way mirroring.

Most of the times, this is done using the RDBMS features like dataguard for Oracle or log shipping for SQLServer. There must be the same feature for DB2/400.

2) The second hard disk will have to be updated in real-time.

This part is done through hardware features like RAID.

This is always set up on you storage layer. You have to decide which kind of RAID to use depending on your security/performances/costs needs.

3) The third hard disk is to be updated with one day delay, which means this hard disk will always hold one day old image so that we can revert to this old image if there is any damages done by any latest transports which cannot be undone easily. We do not want to rely on backup tapes for this because there can be situations where the tapes are faulty and the second reason is tape restoration is very time consuming.

I'm not aware of any disk technology allowing to stage the disk copy writing.

This set up is usually done using database mirroring features.

Best  regards,

Steve.

[Former Member]

Thanks dude!