Re: EMC TimeFinder, and EMC TimeFinder vs Hot Standby

Hi

     For each physical device a BCV is associated. This is at a physical level rather than at logical level. Timefinder is the product which synchronizes these devices and bcvs. Each of these devices and BCVs has a bit map track table to keep track of the disk tracks. This bit map indicates whether a particular disk track has changed or not after the last BCV synchronization operation. During BCV synchronization, timefinder doesn't do dumb copy all the data from primary to BCV. Instead it uses the bit map of disk tracks and copies only the disk tracks that are changed. In a typical VLDB only few percentage of the database changes every day and hence the number of tracks changed are very minimal between backups. Hence the synch process is much faster than regular OS based synchronization mechanism. Not only the backup is faster, also the recovery is faster since only the tracks changed need to be copied from the BCVs to the primary disks.

     SRDF is the product to keep the primary and secondary symmetrix unit in synch using SRDF links, mostly for disaster/site recovery operations. If you set up two sym units to be primary and secondary then all the writes to the primary are propagated to the secondary (synchronously or asynchronously depending upon the setup) and they are kept in synch. For example, if you have primary database in one symmetrix unit and the secondary database in the second symmetrix unit, then since every write to the redo log files are propagated, you could activate the standby database without any data loss (or very minimal loss in rare cases). All these operations are done without any host involvement. You could set up this SRDF writes such that host write system calls will succeed only after the secondary SRDF write confirms the receipt of the data to the primary. But that means performance hit.

     Hope this helps!!

Thanks
Riyaj "Re-yas" Shamsudeen
Certified Oracle DBA
i2 technologies www.i2.com
" These are my opinions. Use at your risk"

                                                                                       
                       
                    Yosi_at_comhill.                                                      
                       
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                    03/21/01                                                           
                       
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Hi All,

Can anyone give me a quick (free!) lesson on the concepts behind timefinder? How does this differ from their standard SRDF which (to my understanding) is to split the mirror and back it up.

Or is it that they add their BCV stuff to SRDF so you can access the data while the mirror is split? Then, is it like a Hot Standby DB?

(We used to get something in high school that was some sort
of mixture between fish and potatoes, and we could never figure out if it was fish or if it was potatoes, or both, or neither. Somehow, this is reminding me of that.)

Thanks loads,

Yosi

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