CA - failover/failback

[avik]

I have continous access running between two EVA3000 boxes that are located at two different locations - primary & DR sites. I understand that incase of a failover, the DR groups will be failed over to the DR site and will be served to the hosts these luns are presented to, at the DR.

Qn 1: The luns presented to the hosts at the DR site should be in read-only mode (or read-write ?) mode before the fail over occurs?. If read-only, do I have to change the mode manually to read-write post failover ?

Also what happens after the failback process ? Will it start replicating the whole data or only the changed blocks back till the point both are in sync so as to failback to source?

[Vic Pratt]

Q1. My testing from a windows system shows that although the replicated data is presented to the failover host, it is not visible to the OS. When I have failed over, CA handles allowing read/write to the replicated data, and reverses the direction of the replication.the original location.
I'm not sure on your second set of questions, but as I understand it, if the failover was for a relatively short duration, failback will not have recopy all the blocks...only what has changed.

[Ivan Ferreira]

R1 - The destination VDISKS (Copy Sets) will be in read only mode until you perform the failover. After the failover, the software will change it to read write and the VDISK that where the source will be changed to read only. You don't need to do this manually.

When you perform the failover, data is continuously replicated, now from the destination to the source (of course, roles change now and you cannot think as destination anymore). No full replication required.

[Uwe Zessin]

> The destination VDISKS (Copy Sets) will be in
> read only mode until you perform the failover.

But that is not the default, is it?
If you configure the system that way, at least Windows will see duplicate devices!

The normal setup is that the presentation is set up on the target Vdisks, but mapping to the host's LUN addresses happens as part of the failover.

[Basil Vizgin]

Uwe, as i remember, readonly targets is on roadmap.
This can be usefull for backup porposes, etc.

[Ivan Ferreira]

Nice Hat Uwe! Congratulations!

>But that is not the default, is it?

Yes, it it's like that by default (At least on my systems)

> If you configure the system that way, at least Windows will see duplicate devices!

No, presentation is not enabled until you perform the failover.

[Uwe Zessin]

I think we are using a different terminology:

we can set up presentation on the target Vdisks, but the disk is not mapped to the host unless a failover is made.
I would not call this a 'readonly mode', because it is confusing.


Making a target Vdisk available to a host in readonly mode for BACKUP (I, too thought that is only on the roadmap, yet) is only good, if you make _very_ sure that the replication has been suspended - else, the backup host will experience unexpected file system changes (similar to what we see every few days here when somebody want to share a file system between two servers, with an operating system that does not know how to do that ;-)

[Ivan Ferreira]

> I think we are using a different terminology:

> we can set up presentation on the target Vdisks, but the disk is not mapped to the host unless a failover is made.
I would not call this a 'readonly mode', because it is confusing.

That is correct, The host cannot access the virtual disk, but if you check the Copy Sets in command view, you will see the disks market as "read only". That was what I mean.

> Making a target Vdisk available to a host in readonly mode for BACKUP (I, too thought that is only on the roadmap, yet) is only good, if you make _very_ sure that the replication has been suspended - else, the backup host will experience unexpected file system changes (similar to what we see every few days here when somebody want to share a file system between two servers, with an operating system that does not know how to do that ;-)

I think that you cannot present the disk to other host while is replicating.

[Uwe Zessin]

> but if you check the Copy Sets in command view,
> you will see the disks market as "read only".
> That was what I mean.

OK, I have assumed so, but don't have a CA setup handy to check. I don't blame you, but it is still confusing like the disk group's so-called "protection level".

> I think that you cannot present the disk to other host while is replicating.

Not today, right. But as I and Basil wrote, it is supposed to be on a roadmap. We'll see...