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Re: backup node question
Thanks for answering my question, Harsh.

regards,
Lin

On Sun, Apr 7, 2013 at 4:05 PM, Harsh J <[EMAIL PROTECTED]> wrote:

> Yes, it need not keep an edits (transactions) stream locally cause
> those are passed synchronously to the BackupNameNode, which persists
> it on its behalf.
>
> On Sun, Apr 7, 2013 at 1:21 PM, Lin Ma <[EMAIL PROTECTED]> wrote:
> > Thanks Harsh,
> >
> > For your comments, "What it means is that the NameNode need not store
> > anything locally", you mean Primary Name Node do not need to store
> > checkpoint/journal locally, and only need to keep memory image up-to-date
> > for edits?
> >
> > regards,
> > Lin
> >
> >
> > On Sun, Apr 7, 2013 at 3:31 PM, Harsh J <[EMAIL PROTECTED]> wrote:
> >>
> >> Hi Lin,
> >>
> >> My reply inline.
> >>
> >> On Sun, Apr 7, 2013 at 12:36 PM, Lin Ma <[EMAIL PROTECTED]> wrote:
> >> > Hi guys,
> >> >
> >> > I am reading from this paper to learn about backup nodes
> >> > (http://www.storageconference.org/2010/Papers/MSST/Shvachko.pdf),
> >> >
> >> > It is mentioned, "It contains all file system metadata information
> >> > except
> >> > for block locations. It can perform all operations of the regular
> >> > NameNode
> >> > that do not involve modification of the namespace or knowledge of
> block
> >> > locations. ", what kinds of operations do not need knowledge of block
> >> > locations?
> >>
> >> Operations that do not involve data reads or writes would not require
> >> knowledge of block locations. Applying also the restriction of no
> >> namespace mutation, an example would be listing directories and
> >> looking up file information via FileStatus objects (perhaps the only
> >> examples - its like a safemode but no reads either).
> >>
> >> > It is also mentioned, "Use of a BackupNode provides the option of
> >> > running
> >> > the NameNode without persistent storage, delegating responsibility for
> >> > the
> >> > namespace state persisting to the BackupNode.", what means "running
> the
> >> > NameNode without persistent storage" and "delegating responsibility
> for
> >> > the
> >> > namespace state persisting"?
> >>
> >> What it means is that the NameNode need not store anything locally,
> >> but can rely on the edits being stored at the BackupNameNode which
> >> would continuously be receiving it. When restarted, it can grab a
> >> current checkpoint from the BNN and boot up anywhere, since there's no
> >> local storage requirement.
> >>
> >> --
> >> Harsh J
> >
> >
>
>
>
> --
> Harsh J
>