Subject: Re: [vserver] HASH FS
From: "Jun OKAJIMA" <okajima@digitalinfra.co.jp>
Date: Sat, 26 Jul 2008 04:34:11 +0900

>
>  Can you compare and contrast your work with the Venti file system from
>  plan9? I believe that it too is a hash-based, write-once, immutable
>  filesystem, isn't it? Or do I misunderstand what you, and they, have done?
>
>

You are right.
Venti and HASH FS have common stuff.
They use hash to share same data.

The biggest difference is,
Venti is used for keeping your own data,
but HASH FS is for existent data.
And, "existent data" is, in short, ready-made disk images for virtual server.

Venti can share same sector between VEs,
but you have to install all files before
you use VE, and you dont have to delete files.
In HASH FS, you dont need any blob installed
before you use.
Blobs are fetched on demand,
and you can delete them any time.

Another merit of HASH FS is,
it is faster, theoretically.

So, if you want to share your own data (like logs)
between VEs, Venti would be a choice,
but you want to share ready-made files (.deb/.rpm),
HASH FS is better.

      --- Okajima, Jun. Tokyo, Japan.
            http://www.machboot.com/
            http://www.digitalinfra.co.jp/