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



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


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