Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261549AbVEPLTL (ORCPT ); Mon, 16 May 2005 07:19:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261545AbVEPLTL (ORCPT ); Mon, 16 May 2005 07:19:11 -0400 Received: from krusty.dt.E-Technik.Uni-Dortmund.DE ([129.217.163.1]:27038 "EHLO mail.dt.e-technik.uni-dortmund.de") by vger.kernel.org with ESMTP id S261523AbVEPLTE (ORCPT ); Mon, 16 May 2005 07:19:04 -0400 Date: Mon, 16 May 2005 13:18:59 +0200 From: Matthias Andree To: linux-kernel@vger.kernel.org Subject: Re: Disk write cache (Was: Hyper-Threading Vulnerability) Message-ID: <20050516111859.GB13387@merlin.emma.line.org> Mail-Followup-To: linux-kernel@vger.kernel.org References: <1115963481.1723.3.camel@alderaan.trey.hu> <20050515145241.GA5627@irc.pl> <200505151121.36243.gene.heskett@verizon.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-PGP-Key: http://home.pages.de/~mandree/keys/GPGKEY.asc User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1569 Lines: 31 On Sun, 15 May 2005, Mikulas Patocka wrote: > Note that disk can still ignore FLUSH CACHE command cached data are small > enough to be written on power loss, so small FLUSH CACHE time doesn't > prove disk cheating. Have you seen a drive yet that writes back blocks after power loss? I have heard rumors about this, but all OEM manuals I looked at for drives I bought or recommended simply stated that the block currently being written at power loss can become damaged (with write cache off), and that the drive can lose the full write cache at power loss (with write cache on) so this looks like daydreaming manifested as rumor. I've heard that drives would be taking rotational energy from their rotating platters and such, but never heard how the hardware compensates the dilation with decreasing rotational frequency, which also requires changed filter settings for the write channel, block encoding, delays, possibly stepping the heads and so on. I don't believe these stories until I see evidence. These are corner cases that a vendor would hardly optimize for. If you know a disk drive (not battery-backed disk controller!) that flashes its cache to NVRAM, or uses rotational energy to save its cache on the platters, please name brand and model and where I can download the material that documents this behavior. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/