Re: [9fans] multiple venti servers

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

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
>