From owner-freebsd-hackers Thu Jul 18 18:40:28 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 747C837B400 for ; Thu, 18 Jul 2002 18:40:25 -0700 (PDT) Received: from mail2.dreamscape.com (mail2.dreamscape.com [206.64.128.18]) by mx1.FreeBSD.org (Postfix) with ESMTP id BA57F43E6A for ; Thu, 18 Jul 2002 18:40:24 -0700 (PDT) (envelope-from krentel@dreamscape.com) Received: from dreamscape.com (sA21-p62.dreamscape.com [209.217.202.62]) by mail2.dreamscape.com (8.9.3+blt/8.9.3) with ESMTP id VAA10079; Thu, 18 Jul 2002 21:40:17 -0400 (EDT) Received: from blue.mwk.domain (localhost [127.0.0.1]) by dreamscape.com (8.11.1/8.11.1) with ESMTP id g6J1da517312; Thu, 18 Jul 2002 21:39:46 -0400 (EDT) (envelope-from krentel@blue.mwk.domain) Message-Id: <200207190139.g6J1da517312@dreamscape.com> To: Peter Wemm Cc: freebsd-hackers@freebsd.org Subject: Re: dump on mounted fs In-Reply-To: Your message of "Wed, 17 Jul 2002 00:33:13 PDT." <20020717073313.9C21D3910@overcee.wemm.org> Date: Thu, 18 Jul 2002 21:39:36 -0400 From: "Mark W. Krentel" 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 > Dump on a live FS is always risky. FreeBSD in 4.x and earlier will have > up to about a 30 second delay before a write() makes it to physical disk. Ok, assume all the writes have finished, we wait 1-2 minutes before starting dump, no new writes happen during the dump, then are we assured that the dump reflects all of the previous writes? I understand there is no perfect solution to backing up a running system. I'm just checking that this isn't way off base. In Linux, the problem is far more serious. No amount of waiting or syncs can force certain writes to be visible to dump. Doesn't happen until umount. I was panicked by this and mainly wanted to check that Freebsd doesn't behave this way. > However, 5.x have snapshots where you can take a virtual snapshot of the > file system device as it existed at the instant that you create it. You can > then take a coherent dump that *will* be accurate. fsck uses snapshots in > 5.x to do background fsck to reclaim lost resources. I guess that's the right long-term solution for backing up a running system. I'm in eager anticipation. --Mark To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message