From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: Date: Sun, 3 Sep 2006 05:53:35 -0700 From: "Tharaneedharan Vilwanathan" To: "Fans of the OS Plan 9 from Bell Labs" <9fans@cse.psu.edu> Subject: Re: [9fans] multiple venti servers In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <44F595DD.30202@village.com> <8ccc8ba40608300802m6708d056qb314d6fd28ebc4ef@mail.gmail.com> Topicbox-Message-UUID: ae57ebf2-ead1-11e9-9d60-3106f5b1d025 Thank you. dharani On 9/1/06, Russ Cox 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 wrote: > > Hi Russ, > > > > On 8/30/06, Russ Cox 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 > > > > > > > >