We have SRDF/A in our environment.
Should we enable session consistency? What is this used for? Can someone give us a few use cases.
My name is Paul and I work in Level 2 of Symmetrix hardware.Most of our customer due use consistency as they
need their R2 side to be consistent in case of a needed failover to bring their hosts and applications up on the
R2 (Remote) side.
Other customers use the remote side as just a backup so they don't have to be fully consistent all the time.
Some of the financial accounts need to always be consistent to be in compliance.
If you are in consistent mode you can drop out if you have un-protected disk drives and a drive drops ready.
Then you would need to do cleanup and re-start SRDF/A again.
It is really up to each individual account and what they are using SRDF/A for.
Please let me know if I can be of assistance with any other details.
Thanks for the reply..
In our scenario we are not able to stay cought up because of limited bandwidth we have.
Most of the time we are about 100-200GB out of sync.
If we enabled session consistency state would we have a consistent data even when the r1-r2 are not in sync?
In your case if you don't have enough bandwidth to sustain and you are always out then you are correct you would never be fully consistent
unless things slowed down and you were able to catch up.
During those slow periods you could catch up but then would drop to not consistent when it got busy again.
So if we enabled "Session consistency state" then will we be able to bring up the hosts on R2 side even when we are not in sync?
From: Paul Bullock <firstname.lastname@example.org<mailto:email@example.com>>
Reply-To: "firstname.lastname@example.org<mailto:email@example.com>" <firstname.lastname@example.org<mailto:email@example.com>>
Date: Mon, 29 Aug 2011 16:21:25 -0400
To: Microsoft Office User <firstname.lastname@example.org<mailto:email@example.com>>
EMC Community Network<https://community.emc.com/index.jspa>
Session Consistency State : Disabled
reply from Paul Bullock<https://community.emc.com/people/PVB9369> in Symmetrix - View the full discussion<https://community.emc.com/message/562595#562595
No sorry. If you are not consistent than the R2 side hosts may have problems.
To be fully in-sync you would need to be consistent.
Sorry if I confused you.
Let us know your exact motive. Are you looking for setting up RESTARTABLE copy of your R2 data ?
If yes, the Consistency should be enabled. Consistency basically means that write ordering and dependent writes are maintained when data is replicated. To put it in simpler words, assume that you encountered a Disk faliure on Source Symm. Due to this one of your R1 is WriteDisabled.
If the Consistency is enabled on the RA Group to which thisDevice belongs, then your replication will stop for all the devices in that RA Group. This will ensure that no new data is written on R2.
Internally, consistency is not as simple as I described. It is managed by the microcode itself.
Yes. I need restartable copy on R2 side at all times.
Even when there are some invalid tracks and devices out of sync.
Is that possible? We do not have sufficient bandwidth to keep us in sync all the time.
There is no use of SRDF A unless you have a bandwidth to support it. A wrong SRDF A setup can lead to extreamly high cache usage.
SRDF AR might be a good option for you but I believe you should contact EMC Services for this. They have a Solution Validation Grp for these things.
I just want to modify Deepak's statement, "SRDF A is infact more useful than SRDF S if bandwidh is less". If you run the below command, it should tell you how much data you are behind the R1 and if r2 data is consistent or not. It does not require consistency to be enabled. I think many ppl in this thread have already discussed the use of consistency so i will not speak about it.
dell2850# symrdf -g test123 query -rdfa
Tracks not Committed to the R2 Side: 0
Time that R2 is behind R1 : 00:00:00
R2 Image Capture Time : N/A
R2 Data is Consistent : Yes