Dhruba Borthakur wrote:
> A good way to implement failover is to make the
Namenode log transactions to
> more than one directory, typically a local directory
and a NFS mounted
> directory. The Namenode writes transactions to both
directories
> synchronously.
>
> If the Namenode machine dies, copy the fsimage and
fsiedits from the NFS
> server and you will have recovered *all* committed
transactions.
>
> The SecondaryNamenode pulls the fsimage and fsedits
once every configured
> period, typically ranging from a few minutes to an
hour. If you use the
> image from the SecondaryNamenode, you might lose the
last few minutes of
> transactions.
That's a good idea. But then, what's the purpose of running
a secondary
namenode, if it can't guarantee that the data loss is
minimal ???
Should't edits be written synchronously to a secondary
namenode, and
fsimage updated synchronously whenever a primary namenode
performs a
checkpoint?
--
Best regards,
Andrzej Bialecki <><
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