Re: Distributed storage. Move away from char device ioctls.

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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 <[email protected]>

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.

	Jeff



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