Re: [9fans] multiple venti servers

["Tharaneedharan Vilwanathan" <vdharani@gmail.com>]

Thank you.

dharani

On 9/1/06, Russ Cox <rsc@swtch.com> wrote:
> wrarena does write every block twice,
> but venti will only write the block to the disk once.
> so it may take twice as long but it should not
> use up twice as much disk space.
>
> russ
>
>
> On 9/1/06, Tharaneedharan Vilwanathan <vdharani@gmail.com> wrote:
> > Hi Russ,
> >
> > On 8/30/06, Russ Cox <rsc@swtch.com> wrote:
> > > > If I am right, one problem with this approach is it becomes tricky
> > > > when both venti servers have updates but yet to be sync'ed. And, in
> > > > particular, when there are identical data backed up (say, I downloaded
> > > > a CD image in two machines and backed up in these two servers), it
> > > > leaves two copies. It may be safe but it does leave two copies.
> > >
> > > You are not right.
> > Good to know I am not right! :-) About 2 years back I tried to
> > reinstall venti server and noticed some pb with copying old data. In
> > response to one of the mails, I had sent this reply:
> >
> > -----------------------------------------------------------------------------
> > From:  vdhar...@infernopark.com - view profile
> > Date:  Mon, Aug 23 2004 11:34 am
> > Email:   vdhar...@infernopark.com
> > Groups:   comp.os.plan9
> > ...
> >
> > i have done similar thing (except fossil) before and i didnt face any
> > problem.
> >
> > but i noticed a couple of things:
> >
> > - if i invoke 'wrarena' twice, it took twice the space. so i think it
> > blindly copies rather than checking for existing data. this raises 2
> > questions: is venti still in good shape (since now two blocks for the same
> > score may exist)? if i backup up same or similar files in different venti
> > servers and later on i merge the venti server data using readarena and
> > wrarena, will it leave duplicate data blocks unnecessarily?
> >
> > - you have to keep the venti score details (vac) seperately all the time.
> > else there is no way to get the signatures and venti may become useless
> > without it.
> > -----------------------------------------------------------------------------
> >
> > Till now, I have been thinking wrarena wrote a copy of every block
> > when I invoked it twice. I think I checked up how much space venti
> > used up but I am not sure whether there was actually some other issue.
> >
> > Thanks
> > dharani
> >
> > >
> > > Since venti coalesces writes, it doesn't matter if both servers sync
> > > to each other.  You'll waste a little bandwidth resending some writes,
> > > but you will not end up with multiple copies of a block on the same
> > > venti server.
> > >
> > > Russ
> > >
> >
> >
>