Re: [RFC][PATCH] dm-cache: block level disk cache target for device mapper

["Eric Van Hensbergen" <ericvh@gmail.com>]

On 11/27/06, bert hubert <bert.hubert@netherlabs.nl> wrote:
> On Mon, Nov 27, 2006 at 06:26:34PM +0000, Eric Van Hensbergen wrote:
> > This is the first cut of a device-mapper target which provides a write-back
> > or write-through block cache.  It is intended to be used in conjunction with
> > remote block devices such as iSCSI or ATA-over-Ethernet, particularly in
> > cluster situations.
>
> How does this work in practice? In other words, what is a typical actual
> configuration?
>
> There is a remote block device, and a local one, and these are kept into
> sync in some way?
>

That's the basic idea.  In our testbed, we had a single iSCSI server
exporting block devices to several clients -- each maintaining their
own local disk cache of the server exported block devices.  You can
configured either write-through or write-back policies -- write-back
has better performance, but somewhat obvious consistency issues in
failure cases.

The original intent was to combine this with the dm-cow target (which
I posted a few hours before the dm-cache patch) to provide a scalable
cluster deployment system based on back-end iSCSI or ATA-over-Ethernet
storage.

          -eric