linux-kernel - Re: [ANNOUNCE] Ramback: faster than a speeding bullet

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Date:	Wed, 12 Mar 2008 09:27:29 -0800
From:	Daniel Phillips <phillips@...nq.net>
To:	tvrtko.ursulin@...hos.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [ANNOUNCE] Ramback: faster than a speeding bullet

On Wednesday 12 March 2008 05:01, tvrtko.ursulin@...hos.com wrote:
> linux-kernel-owner@...r.kernel.org wrote on 10/03/2008 06:46:16:
> 
> > Every little factor of 25 performance increase really helps.
> > 
> > Ramback is a new virtual device with the ability to back a ramdisk
> > by a real disk, obtaining the performance level of a ramdisk but with
> > the data durability of a hard disk.  To work this magic, ramback needs
> > a little help from a UPS.  In a typical test, ramback reduced a 25
> > second file operation[1] to under one second including sync.  Even
> > greater gains are possible for seek-intensive applications.
> 
> What about doing a similar thing as a device mapper target? Have a look a 
> dm-cache, I know that development of that has stopped but it doesn't mean 
> it couldn't be ressurected. It has an advantage that it is generic (any 
> two block devices will do) and you don't need to populate the "cache" on 
> start-up - it happens automatically through cache misses.

It is a device mapper target (though there is no real advantage in that
other than having a handy plug-in api).  It does handle any two block
devices, and it does populate on cache miss.  But also has daemon-driven
population, since it never makes sense to leave the backing disk idle
then have to incur read latency because of that later.

Regards,

Daniel
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