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Date:	Fri, 14 Sep 2007 23:46:51 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Jeff Garzik <jeff@...zik.org>,
	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: Distributed storage. Move away from char device ioctls.

Jeff Garzik wrote:
> Evgeniy Polyakov wrote:
> > Hi.
> >
> > I'm pleased to announce fourth release of the distributed storage
> > subsystem, which allows to form a storage on top of remote and local
> > nodes, which in turn can be exported to another storage as a node to
> > form tree-like storages.
> >
> > This release includes new configuration interface (kernel connector over
> > netlink socket) and number of fixes of various bugs found during move
> > to it (in error path).
> >
> > Further TODO list includes:
> > * implement optional saving of mirroring/linear information on the
> > remote nodes (simple)
> > * new redundancy algorithm (complex)
> > * some thoughts about distributed filesystem tightly connected to DST
> > 	(far-far planes so far)
> >
> > Homepage:
> > http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst
> >
> > Signed-off-by: Evgeniy Polyakov <johnpol@....mipt.ru>
>
> My thoughts.  But first a disclaimer:   Perhaps you will recall me as
> one of the people who really reads all your patches, and examines your
> code and proposals closely.  So, with that in mind...
>
> I question the value of distributed block services (DBS), whether its
> your version or the others out there.  DBS are not very useful, because
> it still relies on a useful filesystem sitting on top of the DBS.  It
> devolves into one of two cases:  (1) multi-path much like today's SCSI,
> with distributed filesystem arbitrarion to ensure coherency, or (2) the
> filesystem running on top of the DBS is on a single host, and thus, a
> single point of failure (SPOF).
>
> It is quite logical to extend the concepts of RAID across the network,
> but ultimately you are still bound by the inflexibility and simplicity
> of the block device.
>
> In contrast, a distributed filesystem offers far more scalability,
> eliminates single points of failure, and offers more room for
> optimization and redundancy across the cluster.
>
> A distributed filesystem is also much more complex, which is why
> distributed block devices are so appealing :)
>
> With a redundant, distributed filesystem, you simply do not need any
> complexity at all at the block device level.  You don't even need RAID.
>
> It is my hope that you will put your skills towards a distributed
> filesystem :)  Of the current solutions, GFS (currently in kernel)
> scales poorly, and NFS v4.1 is amazingly bloated and overly complex.
>
> I've been waiting for years for a smart person to come along and write a
> POSIX-only distributed filesystem.

This http://lkml.org/lkml/2007/8/12/159 may provide a fast-path to reaching 
that goal.


Thanks!

--
Al
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