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

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Message-ID: <20080315202625.GC4193@ucw.cz>
Date:	Sat, 15 Mar 2008 21:26:25 +0100
From:	Pavel Machek <pavel@....cz>
To:	Daniel Phillips <phillips@...nq.net>
Cc:	David Newall <davidn@...idnewall.com>, david@...g.hm,
	Chris Friesen <cfriesen@...tel.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [ANNOUNCE] Ramback: faster than a speeding bullet

On Thu 2008-03-13 12:03:03, Daniel Phillips wrote:
> On Thursday 13 March 2008 12:50, David Newall wrote:
> > Daniel Phillips wrote:
> > > The period where you cannot access the data is downtime.  If your script
> > > just does a cp from a disk array to the ram device you cannot just read
> > > from the backing store in that period because you will need to fail over
> > > to the ramdisk at some point, and you cannot just read from the ramdisk
> > > because it is not populated yet.
> > 
> > Wouldn't a raid-1 set comprising disk + ramdisk do that with no downtime?
> 
> In raid1, write completion has to wait for write completion on all
> mirror members, so writes run at disk speed.  Reads run at ramdisk
> speed, so your proposal sounds useful, but ramback aims for high
> write performance as well.

raid1 + kflushd tweak?

special raid1 mode that signals completion when it hits _one_ of the
drives, and does sync when the slower drive is idle?
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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