From owner-freebsd-hackers Thu Aug 2 10:36: 0 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from sabre.velocet.net (sabre.velocet.net [198.96.118.66]) by hub.freebsd.org (Postfix) with ESMTP id E203437B405 for ; Thu, 2 Aug 2001 10:35:57 -0700 (PDT) (envelope-from dgilbert@office.tor.velocet.net) Received: from office.tor.velocet.net (trooper.velocet.net [204.138.45.2]) by sabre.velocet.net (Postfix) with ESMTP id 7E44B137F33 for ; Thu, 2 Aug 2001 13:35:51 -0400 (EDT) Received: (from dgilbert@localhost) by office.tor.velocet.net (8.11.4/8.9.3) id f72HZpW28352; Thu, 2 Aug 2001 13:35:51 -0400 (EDT) (envelope-from dgilbert) From: David Gilbert MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <15209.36726.676011.413494@trooper.velocet.net> Date: Thu, 2 Aug 2001 13:35:50 -0400 To: Freebsd-hackers@freebsd.org Subject: _real_ ram disk needed ... X-Mailer: VM 6.92 under 20.4 "Emerald" XEmacs Lucid Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG It would seem that the semantics of mfs and md differ signifcantly. If I write data to mfs, it is only sent to swap if it absolutely must --- I chalk this upto the allocations it uses operating like process memory. If I write to md, the speed at which I write to md (swap backed) is limited by the speed of the swap device. It would appear that only a very limited amount of write buffering is going on. Now... I'm dealing with a very poorly designed _binary_ application. It writes out very large sparse matrices to disk (as much as 6G, but randomly between a few hundred meg and 6 gig). It is desireable for the system to _not_ write the blocks in question to disk unless absolutely necessary. Is there any way to make this request to the vm system? For something that fits in memory, the performance of mfs is many dozens of times faster than md. Dave. -- ============================================================================ |David Gilbert, Velocet Communications. | Two things can only be | |Mail: dgilbert@velocet.net | equal if and only if they | |http://www.velocet.net/~dgilbert | are precisely opposite. | =========================================================GLO================ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message