CA (Continuous Access) on XP 512

[Nimesh]

Hi,

I have couple of questions about CA.
1) There are only two options "suspend pair" and "delete(remove) pair" in CA.
2) When I suspend pair, it will force the S-VOL to update with P-VOL.
When I resync this pair, it will do update copy from P-VOL to S-VOL NOT initial (full) copy.

Could any one please varify OR correct the above statements.

Thanks,
Nimesh

[David Navarro]

Hi,
Two points that you say are true.
Only be carefull with resume operation, because only P-vol cylinders modified will be sended to S-vol. That is, if you change something in S-vol while two copies are suspended, when you resumes the pair, these will be different.
In this case, you must do a pairsplit-s and paircreate.

[Nimesh]

When I suspend pair the P-VOL will force S-VOl to sync up. Is this right ?

1) I do modify the P-VOL and do resync then it will do update copy only (not initial/full copy). P-VOL will send the update to S-VOL.

2) If I modify the S-VOL and do resync. Can I able to resync the P-VOL and S-VOL ? Will it be update copy OR initial/full copy?

3) If I modify the P-VOL & S-VOL and do resync. Can I able to resync the P-VOL and S-VOL ? Will it be update copy OR initial/full copy?

Thanks,
Nimesh

[David Navarro]

When I suspend pair the P-VOL will force S-VOl to sync up. Is this right ?

Yes. This is right. Suspend will finish when all changes are updates to S-vol.

1) I do modify the P-VOL and do resync then it will do update copy only (not initial/full copy). P-VOL will send the update to S-VOL.

Yes, Only changes made on P-Vol will be sended to S-vol. At the end you will have the same an both vol's.

2) If I modify the S-VOL and do resync. Can I able to resync the P-VOL and S-VOL ? Will it be update copy OR initial/full copy?

Yes. You can. But only changes on P-vol will be sent to S-vol. That is. you will have a S-vol with changes made on P-vol and change made on S-vol. I understand that this S-vol probably will be inconsistent.

3) If I modify the P-VOL & S-VOL and do resync. Can I able to resync the P-VOL and S-VOL ? Will it be update copy OR initial/full copy?

This question is answered before. Only changes made on P-vol are sent.
CA keeps track of P-vol changes while vol's are suspended, when you resync, updates all the cylinders changed on P-vol to S-vol. If another cylinder on S-vol is changes while the suspention. It will left without update.
In this situation, if you are not sure if the S-vol has been modified, you must delete tha pair and recreate for be sure that all information wil resyncronized again.

I hope it answer you'r questions. Sorry if my english is not very good.

[Ming Zhao · Accepted solution]

When you resync a split CA pair which has the S-VOL write option enabled, the RCU sends the S-VOL cylinder bitmap to the MCU, and the MCU merges the P-VOL and S-VOL bitmaps to determine which cylinders are out-of sync. This ensures proper resynchronization of the pair.

That means even you modify data on S-VOL, after resync, P-VOL and S-VOL will be same.

Regards,