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 >
