Date: Mon, 27 Oct 2014 11:09:40 -0700 From: Kevin Oberman <rkoberman@gmail.com> To: Chris H <bsd-lists@bsdforge.com> Cc: freebsd-stable <freebsd-stable@freebsd.org> Subject: Re: Dump time issues Message-ID: <CAN6yY1sOothUj1i5tTKPHDYNZ%2BCQ3ZKxmYrmq_GE4Ft66LPcBw@mail.gmail.com> In-Reply-To: <6bb4cda435fb420fb663fa1d47b85a08@ultimatedns.net> References: <6978A7BF-3CB7-4088-904D-5A60D755A04C@gmail.com> <20141025113846.GY1235@albert.catwhisker.org> <CAN6yY1tp%2Box6jHVnFJ4m3AYf4bBY-OzEfTnwrBHZZ0wwEARAxg@mail.gmail.com> <6bb4cda435fb420fb663fa1d47b85a08@ultimatedns.net>
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On Mon, Oct 27, 2014 at 9:25 AM, Chris H <bsd-lists@bsdforge.com> wrote: > On Sat, 25 Oct 2014 11:26:44 -0700 Kevin Oberman <rkoberman@gmail.com> > wrote > > > On Sat, Oct 25, 2014 at 4:38 AM, David Wolfskill <david@catwhisker.org> > > wrote: > > > > > On Sat, Oct 25, 2014 at 01:26:43PM +0200, Alban Hertroys wrote: > > > > I?m seeing something odd in my dump output that I didn?t notice > before: > > > > > > > > Dumping /root... > > > > DUMP: WARNING: should use -L when dumping live read-write > filesystems! > > > > > > (That, by the way, is pretty good advice in my experience.) > > > > > > > As long as the volume is not SU+J. Then, in my experience, it's very bad > > advice. > This reminds me of a question that I've been meaning to ask for some > time now; > Why is the FreeBSD install media using SU+J by default? > While I understand Journaling reduces retrieve times, which makes it > all seem more responsive. IMHO the consequences, and limitations it > imposes, seem to outweigh the pro's. > Just wondering... > > --Chris > > I'm aware of two issues with SU+J, one of which is annoying and the other is worse. 1. If the journal is not fully written on power fail or some other reason, you may need to do a full fsck of the volume and the behavior of the system until this is done can be very unpredictable. 2. You can't safely snapshot the system. This is what 'dump -L' does. This means that some files dumped from a live FS may not be consistent (not good!) or, if '-L' is used, the system may well hang. While I love the fast fsck times (2 or 3 seconds) after a crash, I also question the default. Still, it may be a preferred choice be used for very large file systems where a full fsck would take a very long time as long as the risks are understood. For these systems, ZFS might be a better choice. These arguments do NOT favor it being the default, IMHO. -- R. Kevin Oberman, Network Engineer, Retired E-mail: rkoberman@gmail.com
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