Session Consistency State : Disabled

Hello iflaas,

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.

Thank you,

Paul

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?

Hello,

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.

Hello iflaas,

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 >

Reply-To: "jive-553107206-3ucb-2-c23n@emc-developer.hosted.jivesoftware.com " >

Date: Mon, 29 Aug 2011 16:21:25 -0400

To: Microsoft Office User >

Subject: New message: "Session Consistency State : Disabled"

EMC Community Network

Session Consistency State : Disabled

reply from Paul Bullock in Symmetrix - View the full discussion

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.

Regards

DpK

Hi,

There are couple of things you should keep in mind before you enable consistency:

1) Do you have multiple source Symms replicating to one or more targets?

2) Do you have a Composite group?

Write ordering and dependency write is taken care by SRDF. You dont need to enable consistency option to get write ordering/dependency writes. Consistency will help you in cases where you have multiple RA groups and if one link goes down, its going to suspend the other link also so the R2 site remains consistent. This is just one of the example. For more information please refer to the SRDF guide for more details.

regards,

Saurabh Rohilla

HI,

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

.

.

.

regards,

Saurabh Rohilla

Sourab,

Can you clarify "suspend the other link" scenario? Is it when Single R1 and multiple R2(two different target array)

Hi,

In this picture, if one link or RA group is down, consistency will suspend the replication on the other link also.

regards,

Saurabh