From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.bitfolk.com (use.bitfolk.com [85.119.80.223]) (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 0544B21C16A for ; Thu, 11 Dec 2025 00:42:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=85.119.80.223 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765413732; cv=none; b=GkXCgr/FHK5PbeDGIzAfaFZ/yySXppQxpm2BQWr8DU5xGUiewWlIn6hz4q4/1msIX/IbvaXNYj/POklvaXynQNRLnl9nNRXJCrNdEt8CxfzFCU6IE6lqzlUbGQgw8ZHvYN2aaijSlR8k7JeJErEoTPW+OO7EKLjHre577Vc5xbs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765413732; c=relaxed/simple; bh=qhIaQPtd0SescODI788eomBjcpXjhPGL1nDQ9gpaZ2E=; h=Date:From:To:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PsyjZQGcBllhAs6x992TOV5A1MPtcgJlN8NMg6wZDfat9m3iQsTy1yDd9fBhhu8LXgN/x9WrGP1Ct0hxTKERnKN4bbeJMmqCnMT1xfax4N5ilaNGLj3LEVxDhd1FGL0CGwYD73+Q6FSNPDMyLKOC1LAnFc4j4Q2jgTYD4eKbHDk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=strugglers.net; spf=pass smtp.mailfrom=strugglers.net; dkim=pass (2048-bit key) header.d=strugglers.net header.i=@strugglers.net header.b=op0AUpbe; arc=none smtp.client-ip=85.119.80.223 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=strugglers.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=strugglers.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=strugglers.net header.i=@strugglers.net header.b="op0AUpbe" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=strugglers.net; s=alpha; h=In-Reply-To:Content-Type:MIME-Version:References :Message-ID:Subject:To:From:Date:Content-Transfer-Encoding:Sender:Reply-To:Cc :Content-ID:Content-Description:Resent-To; bh=NKrZFz+4Dl2O9buccJbaUlKbE0pgbGHJ/3Qet4d4wbo=; b=op0AUpbevMCdT6Pi8VDNUmXQZM Xq9kLsTJMlaZ4MJ9QPG4FJ97dKdARQidP/y8C06dnrU774+zLfJQF0WYzqiinKalIAcrd65iWj9NI J5xppciSvB604ffuoYY9Qh7Cjdbm+RlZtgOhqAjLnZgN5onY+g1d3Jfg8fbP1VnCD2RPFoZbNqlSh dCSr4TMQ/xWsezuS9vEvJJAz2FbJsML6zMGBPFUdkIUulARRrQUDxdzVjiFZKWoMdkrnbV/986+Er U6+UYPMWBBypyv7kgCRn/TsXurW+QlQYYYYwtejK7L5VlBXsT3EtG9kksKXlISWnASVxlKO3ZRlBw Oh4wTIgg==; Received: from andy by mail.bitfolk.com with local (Exim 4.94.2) (envelope-from ) id 1vTUUt-0002lB-VD for linux-raid@vger.kernel.org; Thu, 11 Dec 2025 00:25:31 +0000 Date: Thu, 11 Dec 2025 00:25:31 +0000 From: Andy Smith To: "linux-raid@vger.kernel.org" Subject: Re: Possible issue with software RAID 1 in case of disks with different speed Message-ID: Mail-Followup-To: "linux-raid@vger.kernel.org" References: Precedence: bulk X-Mailing-List: linux-raid@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: OpenPGP: id=BF15490B; url=http://strugglers.net/~andy/pubkey.asc X-URL: http://strugglers.net/wiki/User:Andy X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: andy@strugglers.net X-SA-Exim-Scanned: No (on mail.bitfolk.com); SAEximRunCond expanded to false Hi, On Sun, Dec 07, 2025 at 02:41:37PM +0000, Christian Focke-Kiss wrote: > Conclusion: > I suspect software RAID 1 has issues if one disk of a three disk RAID 1 > set is significantly slower than the other two disks. As others have mentioned I suspect your problem is USB. At no point in the last 25 years have I found it a reliable way to have permanently attached storage. Storage with wildly different latency isn't a great setup but I haven't found MD RAID-1 to have a big problem with it, not to the point of instability. write-mostly hasn't tended to have a huge effect for me unless the two devices are radically different in performance. MD RAID already sends reads to the device with the lowest amount of pending IO so all else being equal, if you pair a SSD with a HDD, the SSD will get more reads because they will complete sooner. Though do note that with RAID-1 a single sequential read will all come from one device. It is only when there are multiple threads reading that balancing can take place. Thanks, Andy -- https://bitfolk.com/ -- No-nonsense VPS hosting