[9fans] multiple venti servers

[9fans] multiple venti servers

[John Floren]

Hi, I've got a quick question
If I set up several Venti servers, is it possible to split up backups
among the various servers? A kind of networked RAID, if you will.

John
-- 
"The first thing we do, let's kill all the lawyers" -- Shakespeare, Henry VI

Re: [9fans] multiple venti servers

[Russ Cox]

You could write a pretty simple proxy that would behave
as a composite of multiple venti servers, and then split
up blocks among the servers based on the low bits of their scores.
Of course now you have multiple single points of failure.
I suppose if you were really clever you could do something
like have five venti servers and send each block to two of them.

If you use the new venti libraries (which speak the same protocol)
writing a proxy is pretty easy.  See
http://swtch.com/usr/local/plan9/src/cmd/venti/ro.c
for example.

Russ

Re: [9fans] multiple venti servers

[geoff]

An alternative might be to run venti/copy from your main venti server
to a backup venti server(s) periodically.

Re: [9fans] multiple venti servers

[Wes Kussmaul]

geoff@plan9.bell-labs.com wrote:
> An alternative might be to run venti/copy from your main venti server
> to a backup venti server(s) periodically.
>   
If you made an arrangement with Chris Gladwin at Cleversafe you could 
avoid having to own and manage those dispersed servers.

http://www.cleversafe.com/

Re: [9fans] multiple venti servers

[Francisco J Ballesteros]

At urjc we have a single venti server, backed up into another venti server
at a different machine. Each night we copy the changes from one venti to another
 using a script.

Just to say that what geoff suggested works pretty well for us. Of
course, at worst
case, you loose a whole day of work.

On 8/30/06, Wes Kussmaul <wes@village.com> wrote:
> geoff@plan9.bell-labs.com wrote:
> > An alternative might be to run venti/copy from your main venti server
> > to a backup venti server(s) periodically.
> >
> If you made an arrangement with Chris Gladwin at Cleversafe you could
> avoid having to own and manage those dispersed servers.
>
> http://www.cleversafe.com/
>
>
>

Re: [9fans] multiple venti servers

[Tharaneedharan Vilwanathan]

Hi,

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.

Thanks
dharani

On 8/30/06, Francisco J Ballesteros <nemo@lsub.org> wrote:
> At urjc we have a single venti server, backed up into another venti server
> at a different machine. Each night we copy the changes from one venti to another
>  using a script.
>
> Just to say that what geoff suggested works pretty well for us. Of
> course, at worst
> case, you loose a whole day of work.
>
> On 8/30/06, Wes Kussmaul <wes@village.com> wrote:
> > geoff@plan9.bell-labs.com wrote:
> > > An alternative might be to run venti/copy from your main venti server
> > > to a backup venti server(s) periodically.
> > >
> > If you made an arrangement with Chris Gladwin at Cleversafe you could
> > avoid having to own and manage those dispersed servers.
> >
> > http://www.cleversafe.com/
> >
> >
> >
>

Re: [9fans] multiple venti servers

[William Josephson]

On Wed, Aug 30, 2006 at 09:01:00AM -0700, Tharaneedharan Vilwanathan 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.

Writes presumably only go to the master.

Re: [9fans] multiple venti servers

[LiteStar numnums]

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On 8/30/06, William Josephson <jkw@eecs.harvard.edu> wrote:
>
> [SNIP]
> Writes presumably only go to the master.
>
Plus, if writes went only to the master & you had two machines backing up
the same thing to the same venti server, it wouldn't be a problem because
the sha1 has would be the same & thus venti wouldn't store it. So it should
be:
 clients -> master venti -> backup cloud of ventii.


-- 
If work and leisure are soon to be subordinated to this one utopian
principle -- absolute busyness -- then utopia and melancholy will come to
coincide: an age without conflict will dawn, perpetually busy -- and without
consciousness.

-- Günter Grass

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Re: [9fans] multiple venti servers

[Francisco J Ballesteros]

We start the second venti server (the backup) just to update its
arenas with those
of the primary one. Also, we format a fossil on the backup machine so
we could boot
it upon failures of the primary.

All clients write to the primary file server (fossil) which has just
one venti on its own
machine. This is the venti backed up to our secondary venti (once per night).

On 8/30/06, William Josephson <jkw@eecs.harvard.edu> wrote:
> On Wed, Aug 30, 2006 at 09:01:00AM -0700, Tharaneedharan Vilwanathan 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.
>
> Writes presumably only go to the master.
>
>

Re: [9fans] multiple venti servers

[Robert Raschke]

Francisco wrote:
> We start the second venti server (the backup) just to update its
> arenas with those
> of the primary one. Also, we format a fossil on the backup machine so
> we could boot
> it upon failures of the primary.
> 
> All clients write to the primary file server (fossil) which has just
> one venti on its own
> machine. This is the venti backed up to our secondary venti (once per night).
> 

Yup, that's my approach as well.  I just start up a venti on my
(otherwise "diskless") terminal and then run a backup script on the
main server.  I got the backup script from somewhere Russ inspired,
but for the life of me cannot remember where exactly:

#!/bin/rc

rfork e
. bkup.info
fn x {
	echo x $*
	y=$1
	if(~ $#$y 0){
		$y=0
	}
	echo venti/wrarena -h other_venti_hostname -o $2 $3 $$y
	end=`{venti/wrarena -h other_venti_hostname -o $2 $3 $$y | grep '^end offset ' | sed 's/^end offset //'}
	if(~ $#end 1 && ! ~ $$y $end){
		$y=$end
		echo '#' `{date} >>bkup.info
		whatis $y >>bkup.info
	}
}
hget http://127.1:8000/index | 
awk '
/^index=/ { blockSize=0+substr($3, 11); }
/^arena=/ { arena=substr($1, 7); }
/^	arena=/ { start=0+substr($5, 2)-blockSize; printf("x %s %d %s\n", arena, start, $3); }
' |rc


This copies the latest blocks from your main venti to your running
backup one.  On the backup machine you can then do whatever you want
with the venti.  For example create yourself a fossil, and as long as
you make sure that fossil doesn't snap to the venti, you'll always
have a nice pristine copy of your original.

Robby

Re: [9fans] multiple venti servers

[Russ Cox]

> 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.

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

Re: [9fans] multiple venti servers

[Tharaneedharan Vilwanathan]

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
>

Re: [9fans] multiple venti servers

[Russ Cox]

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
> >
>
>

Re: [9fans] multiple venti servers

[Tharaneedharan Vilwanathan]

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
> > >
> >
> >
>