Re: Data Mirroring on two data centers -- How to use ASM ?

One more reason to use data guard instead of storage/LVM level replication in high-activity OLTP environments is that redolog entry based shipping is much more more fine grained than storage block level replication.

I once asked one EMC admin, they told that the minimum block size for SRDF is 32k. So if you update one row and commit, you'd need to ship few hundred bytes to standby, while with SRDF you'd need to transfer 32 kilobytes over the fibre when the block is written to disk plus you need to continuously transfer redolog writes before the datafile blocks are sent to remote.

If your management definitely requires SAN based replication, then you could just keep your archivelogs on a replicated volume/storage and do frequent log switches to keep the lag small in case of primary failure.

Tanel.

• Original Message ----- From: Carel-Jan Engel To: db.mail.1_at_gmail.com Cc: oracle-l_at_freelists.org Sent: Saturday, May 20, 2006 3:06 AM Subject: Re: Data Mirroring on two data centers -- How to use ASM ?

  Hi Madhu,

  I'm wondering your primary 'requirement' of mirroring data across TWO data centers.

  IMHO, mirroring between data centers is a solution, or if you like, tool. Whatever, it isn't a requirement.

  Requirements could be something like:

• After a server failure, the database should be available again within 30 minutes
• After a server failure, no more than 5 minutes worth of transactions may be lost
• After a database corruption, the database should be available again within 6 hours
• After a database corruption, no more than 30 minutes of transactions may be lost
• Restoring of the database to any point in time between now and now - 6 days must be possible

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