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Re: backup node question
Lin Ma 2013-04-07, 07:51
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?


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