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@comhill.
com To: Multiple recipients of list ORACLE-L
<[EMAIL PROTECTED]>
Sent by: cc:
root@fatcity. Subject: EMC TimeFinder, and EMC
TimeFinder vs Hot Standby
com
03/21/01
05:10 AM
Please
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ORACLE-L
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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