Storage replica

[Taifur]

Hi

I will do stroage replication from DC site to DR site .Two kinds of replica is possible which are sync replica and Async replica. My query is which replica is better from DC site to DR site

Pls let me know about it.

Rgds//
Taifur

[g3jza]

Hi,
it depends:

application performance on the primary site vs. data currency /non-currency of the data on the secondary site.

When doing asynchronous replication between 2 distant disk arrays, then the performance of the applications on the primary site isn't affected, as the I/O on the primary site is acknowledged immediately.

When doing synchronous replication, then the performance of the applications on the primary site is affected, as the I/O operation on the primary site's disk array has to wait until the write operation completes on the secondary disk array on the DR site.

So you need to know what you want to sacrifice.

I don't know what kind of disk arrays are you using, but you should probably have a look at Continuos Access XP (CA XP) manual on docs.hp.com if you have HP XP's disk arrays.

[InterceptorF]

Agreed.

 Asynch is FASTER, Sync is SLOWER 

Async is faster because it doesn't need the an 'ACK' to write the data to the SVOL. It just does.

Sync is slower because it must validate with an 'ACK' that the SVOL  has written before the PVOL will -- and THEN it will validate PVOL and SVOL are the same. If it isn't it will rollback the SVOL and again validate both the PVOL and SVOL are the same.  << all that extra checking takes time. 

So depending on the business model you are using, speedy backups may be the way to go but if you must have a validated copy on the SVOL, you will need to go Sync.