SnapMirror synchronous or asynchronous question

[OLIVERLEACH]

Just need some clarification on a couple of points around SnapMirror in synchronous or asynchronous mode:

1 - How can I set up SnapMirror to do asynchronous mirroring? Is there a setting somewhere I need to configure to tell SnapMirror to run asynchronously?

2 - What happens if a block does not get copied when using asynchronous mirroring? Does the whole lun or volume I am copying become corrupted as that 1 block is missing? How does NetApp work around this?

Many thanks

Oli

[aborzenkov]

You set sync or asycn in /etc/snapmirror.conf. Default is async.

SnapMirror async transfers snapshots. Until snapshot is completely transferred you always see previous volume state. If there was error during transmission, it will retry from the last check point.

[spence · Accepted solution]

How about you start with this : http://www.netapp.com/us/media/tr-3446.pdf and http://www.netapp.com/us/media/tr-3326.pdf

Q: How can I set up SnapMirror to do asynchronous mirroring? Is there a setting somewhere I need to configure to tell SnapMirror to run asynchronously?

A: It does Async by default.  You have to make config entries for sync and semi-sync.

Q: What happens if a block does not get copied when using asynchronous mirroring? Does the whole lun or volume I am copying become corrupted as that 1 block is missing? How does NetApp work around this?

A: SnapMirror is a TCP\IP based technology, thus transmission is ensured based up the IP stack.  If extra paranoid you enable checksums.

[OLIVERLEACH]

Thanks guys. Appreciate your answers.