From: Daniel Phillips <phillips@phunq.net>
To: david@lang.hm
Subject: Re: [ANNOUNCE] Ramback: faster than a speeding bullet
Date: Mon, 17 Mar 2008 00:16:18 -0800
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Cc: David Newall <davidn@davidnewall.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Willy Tarreau <w@1wt.eu>, linux-kernel@vger.kernel.org
References: <200803092346.17556.phillips@phunq.net> <200803162252.58274.phillips@phunq.net> <alpine.DEB.1.00.0803162341340.14887@asgard.lang.hm>
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On Sunday 16 March 2008 23:49, david@lang.hm wrote:
> > Mirroring on the other hand, makes a realtime copy of a volume, that is
> > never out of date.
> 
> so just mirror to a local disk array then.

Great idea.  Except that the disk array has millisecond level latency,
when what we trying to achieve is microsecond level latency.

> a local disk array has more write bandwidth than a network connection to a 
> remote machine, so if you can mirror to a remote machine you can mirror to 
> a local disk array.

So you could potentially connect to a _huge_ disk array and write deltas
to it.  The disk array would have to support roughly 3 Gbytes/second of
write bandwidth to keep up with the Violin ramdisk.  Doable, but you are
now in the serious heavy iron zone.

Personally, I like my nice simple design a lot more.  Just mirror it, as
many times as you need to satisfy your paranoia.  Or how about go write
your own?

Daniel
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