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 >
