From owner-freebsd-stable Sat May 5 9:31:19 2001 Delivered-To: freebsd-stable@freebsd.org Received: from quack.kfu.com (quack.kfu.com [205.178.90.194]) by hub.freebsd.org (Postfix) with ESMTP id 682AA37B423 for ; Sat, 5 May 2001 09:31:16 -0700 (PDT) (envelope-from nsayer@quack.kfu.com) Received: from morpheus.kfu.com (morpheus.kfu.com [3ffe:1200:301b:1:2d0:b7ff:fe3f:bdd0]) by quack.kfu.com (8.11.3/8.11.3) with ESMTP id f45GV9c20530 (using TLSv1/SSLv3 with cipher EDH-RSA-DES-CBC3-SHA (168 bits) verified OK); Sat, 5 May 2001 09:31:15 -0700 (PDT) (envelope-from nsayer@quack.kfu.com) Received: from quack.kfu.com (localhost [127.0.0.1]) by morpheus.kfu.com (8.11.3/8.11.3) with ESMTP id f45GV9u20820; Sat, 5 May 2001 09:31:09 -0700 (PDT) (envelope-from nsayer@quack.kfu.com) Message-ID: <3AF42ACD.5000500@quack.kfu.com> Date: Sat, 05 May 2001 09:31:09 -0700 From: Nick Sayer User-Agent: Mozilla/5.0 (X11; U; FreeBSD 4.3-RELEASE i386; en-US; 0.8.1) Gecko/20010411 X-Accept-Language: en-GB, en-US, en MIME-Version: 1.0 To: Doug Russell Cc: stable Subject: Re: soft update should be default References: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-freebsd-stable@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Doug Russell wrote: > On Sat, 5 May 2001, Cy Schubert - ITSD Open Systems Group wrote: > > >> Of course as Gordon writes above, all bets are off if your disk does >> write-caching. > > > I still don't totally understand this. In the case of a drive with WCE, > aren't we always assuming that the drive will correctly write the data out > eventually, even if the system crashes? Yes. But that assumption is flawed. > > This assumes that we aren't talking about a power failure, here, but if it > is an external drive array with dual power supplies, at least one battery > backed, it doesn't matter even if the compuer power is cut, the drive > should still eventually flush out it's cache, shouldn't it? That may be the original intent, but cheap IDE drives let you turn on write caching, and they're for sure not battery-backed (nor do they attempt to store enough power at power-off to write back the cache with the remaining rotational latency or any such trickery). They lie about it. Write caching is evil unless you specifically know that it's being battery backed. 99.44% of the time, that's not the case. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message