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Continuous Access "Failsafe" mode

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Sean OB_1
Honored Contributor

Continuous Access "Failsafe" mode

Howdy,

I'm reading the CA admin guide and don't quite understand this.

Failsafe mode
The failsafe mode specifies how host writes and remote replication behave when a group member
fails. The failsafe mode can be either:

• Failsafe enabled–If any virtual disk within the DR group fails or becomes unreachable, all host
writes and remote replication automatically stop. This preserves the order of the replicated data.
A failsafe–enabled DR group can be in one of two states:
• Locked (failsafe–locked)–Host writes and remote replication automatically stop.
• Unlocked (failsafe–unlocked)–Host writes and remote replication occur.
• Failsafe disabled–If any destination virtual disk (remote copy) within the DR group fails or
becomes unreachable, all host writes to the source DR group continue, but all remote replication
to the destination DR group automatically stops; the source DR group logs its host writes to the
DR group log until remote replication is re–established. If a source virtual disk fails, host writes
to the failed disk stop, as well as remote replication to its remote copy; host writes and remote
replication to the other members of the DR group continue normally.

Are there 3 modes?

Failsafe enabled Locked
Failsafe enabled Unlocked
Failsafe disabled


Can someone explain what happens in all three modes when a source virtual disk fails?

Can someone explain what happens in all three modes when a destination virtual disk fails?

TIA and points for
4 REPLIES
Sean OB_1
Honored Contributor

Re: Continuous Access "Failsafe" mode

Whoops meant to add more.

Are is are there only two modes:

Failsafe enabled
Failsafe disabled

and when it's enabled it is set to unlocked if all virtual disks are accessible and in the event of any failure of a virtual disk it's set to locked and all access stops?

Uwe Zessin
Honored Contributor
Solution

Re: Continuous Access "Failsafe" mode

No, there are only two modes:
- failsafe disabled
- failsafe enabled

The second mode can have two different states:
- unlocked
-- host writes and remote replication works
- locked
-- there was an error and host writes and
-- remote replication has been stopped


The idea of the failsafe mode is that the data on source and destination must always been identical. For example, if the connection between the storage array has broken, all host writes will be blocked and there is no write history logging.
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Sean OB_1
Honored Contributor

Re: Continuous Access "Failsafe" mode

So with failsafe enabled when there is a failure in either the source or destination ALL writing to the arrays(source and destination) is stopped for all disks in the DR Group?

Can you give me an example of when this mode would be used?

Uwe Zessin
Honored Contributor

Re: Continuous Access "Failsafe" mode

Yes, that's what I read from the manual. So far I didn't have any time to try this feature out in our lab for reasons explained below ;-)

The failsafe mode would only be used on explicit customer request - see the last paragraph in my previous message. Most customers don't have that extreme integrity requirements and rather have their processing continue, but the feature is there.
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