From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52AAA3D16EC for ; Fri, 1 May 2026 19:47:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777664859; cv=none; b=jBkx0MeCMRPGLgeN5LFDgdzUPADXNlc8nuuIPfb3stfCAZXWzA2WtxQHgbW7SRLIQ26pXKbUgA2gpj84CPysBF0L8NlcNCdu1U/+1F5zW1fRHxMiCs+owrFCCnEjr7R2+7BjLybtUy8aJFCxykNI9R1F2KCqSHUPmCWd3SqP17U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777664859; c=relaxed/simple; bh=tTQxO1HFYqK2qYnCcDIbyhe18U+8nD8zRgYvECcGKNA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CM4L7de0XzO2uZjbGq0ohGNFn09cjwuD5WqXy4nlqtBc/d0lg0fcZIYZ8OcNdw37JMKvU+2/CBFMjPMS77ZhqKffejZLOUfeirOwez6U8lUW4OxJZ/apZDs2k2Q41Z5JLSRGQXOo4KZWnPptazrrnHepv02ycCiPZjdKoHWtASY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=uRAZUPir; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="uRAZUPir" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=GJ+oYQjemozvwpJlGqadgjG7lpeLN4I9Uzkg/dcZqmg=; b=uRAZUPire5BuHvjS4AaJDx39To DvXtIvSGEk3YT/ZoeHwMdzWRvjcnishSVw6/wHiQjTUBbNwR84SGUlr9RaX9CqAw8jhtzTZ/lpZat 6h6iAz6FMOeP0D0P4RS0pmCASYgHTPNKQngMO5Y7LvK80FY05PGru28d8MZAqPpmFldWcmOHcL2+J HotuX2+V5sx2fPFS5xjpiAYtsIg6Q7Vbc0c+c4QUNY0cjlYGjjKgsxYKGZ4UAeZjV91PcESi9G3nI lybRmozIG7wlZSJl7oE6+0Yy48dckuwhjcGLhg/ezwreOQsVyV+lP9g40YKqQJdS/XvX/9BgVNJQC BmowYGkg==; Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1wItpn-00000009Fkj-1HYP; Fri, 01 May 2026 19:47:35 +0000 Date: Fri, 1 May 2026 20:47:35 +0100 From: Matthew Wilcox To: Haris Iqbal Cc: lsf-pc@lists.linux-foundation.org, linux-block@vger.kernel.org, Jia Li Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] A block level, active-active replication solution Message-ID: References: Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Feb 03, 2026 at 04:09:59PM +0100, Haris Iqbal via Lsf-pc wrote: > We are working on a pair of kernel modules which would offer a new > replication solution in the Linux kernel. It would be a block level, > active-active replication solution for RDMA transport. Why is active-active a good idea? With an active-passive solution, network traffic is directed to the active node. Over time at some point we get close to saturating the link and performance drops. At that point, human intervention will occur and the network link will be upgraded. With an active-active solution, traffic goes to each node. At smoe point each link will be about 75% utilised and we won't see any performance problems. But then a node goes down and all of a sudden the remaining node is being hit with 150% of the link capacity. There's no gradual degradation here; the whole solution just goes down. Of course it doesn't have to be network capacity either; it could be CPU, RAM or any other resource needed to service the requests. Active-active is fragile and I would never recommend such a solution. I won't be in your session, but I thought it worth raising this point.