From owner-freebsd-small Tue Apr 4 11:37:12 2000 Delivered-To: freebsd-small@freebsd.org Received: from rover.village.org (rover.village.org [204.144.255.49]) by hub.freebsd.org (Postfix) with ESMTP id DD48337B82D for ; Tue, 4 Apr 2000 11:37:06 -0700 (PDT) (envelope-from imp@harmony.village.org) Received: from harmony.village.org (harmony.village.org [10.0.0.6]) by rover.village.org (8.9.3/8.9.3) with ESMTP id MAA93356; Tue, 4 Apr 2000 12:37:05 -0600 (MDT) (envelope-from imp@harmony.village.org) Received: from harmony.village.org (localhost.village.org [127.0.0.1]) by harmony.village.org (8.9.3/8.8.3) with ESMTP id MAA70239; Tue, 4 Apr 2000 12:36:22 -0600 (MDT) Message-Id: <200004041836.MAA70239@harmony.village.org> To: "Jeffrey S. Sharp" Subject: Re: Mounting and Corruption Rehashed Cc: "freebsd-small" In-reply-to: Your message of "Tue, 04 Apr 2000 14:16:05 CDT." <001f01bf9e6a$3a0b3c00$2aa85c0a@vulcan> References: <001f01bf9e6a$3a0b3c00$2aa85c0a@vulcan> Date: Tue, 04 Apr 2000 12:36:22 -0600 From: Warner Losh Sender: owner-freebsd-small@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG In message <001f01bf9e6a$3a0b3c00$2aa85c0a@vulcan> "Jeffrey S. Sharp" writes: : Let's set the way-back knob to a few months ago. We were discussing the : viability of doing the following: : : * Mounting flash read-only on / : * Mounting small MFS filesystems on /var and /tmp : * Temporarily remounting / read-write to make changes : : The problem was this little paragraph from `man mount`: : : > Switching a filesystem back and forth between asynchronous : > and normal op­eration or between read/write and read/only : > access using ``mount -u'' may gradually bring about severe : > filesystem corruption. : : Someone spoke up and said that they had actually experienced this : corruption. I've not seen corruption. However, I oly change one or two files somewhat infrequently and tend to reboot often when I'm changing the underlying filesystem. : Please excuse me if the following is a dumb question: why even mount the : flash _read-only_ in the first place? If /var and /tmp are on separate : filesystems (MFS), what write operations are going to happen to the flash : that mounting read-only would prevent? The superblock gets updated from time to time. Also, when things are mounted r/o you can power off at any time and know that the filesystem will be stable when you come back. I've had some problems in the past where I've trashed a filesystem that was mounted r/w by doing this at just the wrong time even though there wasn't much activity. Mounting R/O ensures that you don't accidentally do writes as well. Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-small" in the body of the message