[9fans] Query regarding vac

[9fans] Query regarding vac

[anooop.anooop]

Hello All,

I was using venti/write to store off small data sets which are less
than a datablock in size earlier. But now I have started using vac for
larger data but I have come across this problem:

Writing the same datablock to the venti server used to give me the
same score always. But vac does not have that property. If I store the
same file many times it gives me different scores.

for eg:
using venti/write
---------------
anoopm@anoopm-laptop:~/workspace/ServerBackEnd$ ./write -h 127.0.0.1 <
msg
00ef06474fb2fe5720eb39eb86c85d96f00362e2
anoopm@anoopm-laptop:~/workspace/ServerBackEnd$ ./write -h 127.0.0.1 <
msg
00ef06474fb2fe5720eb39eb86c85d96f00362e2
anoopm@anoopm-laptop:~/workspace/ServerBackEnd$ ./write -h 127.0.0.1 <
msg
00ef06474fb2fe5720eb39eb86c85d96f00362e2

using vac
-------------
anoopm@anoopm-laptop:~/workspace/ServerBackEnd$ ./vac -h 127.0.0.1
msg
vac:5563f21a3f4d1b783175d57b029ca7d0f210d036
anoopm@anoopm-laptop:~/workspace/ServerBackEnd$ ./vac -h 127.0.0.1
msg
vac:49c3411166ad14afc30d5d3b6a5ec487ce9246d7
anoopm@anoopm-laptop:~/workspace/ServerBackEnd$ ./vac -h 127.0.0.1
msg
vac:977e275c94de5ce6d03163ff85243e29531f961b

>From vac's man page "When vac is used on a file tree that shares data
with an existing archive, the consumption of storage will be
approximately equal to an incremental backup"

But then why does it give different scores each time?

This might be an expected behaviour. But can any of you please suggest
a work around for my problem?

Thanks in advance.

Regards,
Anoop

Re: [9fans] Query regarding vac

[roger peppe]

2009/2/19  <anooop.anooop@gmail.com>:
> Hello All,
>
> I was using venti/write to store off small data sets which are less
> than a datablock in size earlier. But now I have started using vac for
> larger data but I have come across this problem:
>
> Writing the same datablock to the venti server used to give me the
> same score always. But vac does not have that property. If I store the
> same file many times it gives me different scores.

that's probably because vac stores the metadata about
the file as well as the file itself. the score is probably
different because the access time of the file has changed.

if you really always want the same score for the same
file, i think you'll probably have to hack vac to do what you
want (it shouldn't be hard - either just write the file data itself,
or zero selected metadata).

Re: [9fans] Query regarding vac

[anooop.anooop]

> that's probably because vac stores the metadata about
> the file as well as the file itself. the score is probably
> different because the access time of the file has changed.
>
> if you really always want the same score for the same
> file, i think you'll probably have to hack vac to do what you
> want (it shouldn't be hard - either just write the file data itself,
> or zero selected metadata).

Thank you.
I was hoping that there will be some option that might help.. It does
not hinder my work altogether, so I will leave it for now. I am behind
schedule and really short of time to hack the vac now otherwise I
would have given a try. :-)

~Anoop