Date: Mon, 26 Jul 2004 21:53:02 +0000 From: bugghy <bugghy@home.ro> To: freebsd-current@freebsd.org Subject: Re: magic sysrq keys functionality Message-ID: <1090878779.715.18.camel@illusion.com> In-Reply-To: <20040726181821.GB96815@green.homeunix.org> References: <1090718450.2020.4.camel@illusion.com> <200407251112.46183.doconnor@gsoft.com.au> <1090790611.4628.1.camel@illusion.com> <20040726152151.GC1473@green.homeunix.org> <20040726114142.E32601@pooker.samsco.org> <20040726175219.GA96815@green.homeunix.org> <20040726121005.D32601@pooker.samsco.org> <20040726181821.GB96815@green.homeunix.org>
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So, what would be a convenient way to protect a 5.x release against data loss / corruption in case of frequent powerfaillures. (a software method) On Mon, 2004-07-26 at 18:18, Brian Fundakowski Feldman wrote: > On Mon, Jul 26, 2004 at 12:15:02PM -0600, Scott Long wrote: > > On Mon, 26 Jul 2004, Brian Fundakowski Feldman wrote: > > > On Mon, Jul 26, 2004 at 11:49:55AM -0600, Scott Long wrote: > > > > On Mon, 26 Jul 2004, Brian Fundakowski Feldman wrote: > > > > B> On Sun, Jul 25, 2004 at 09:23:36PM +0000, bugghy wrote: > > > > > > Yeah but it sometimes "freezes" (no reboot) ... and I'd rather umount my > > > > > > filesystems before rebooting. > > > > > > > > > > SoftUpdates guarantess that your file systems will not get corrupt. > > > > > > > > > > > > > This isn't entirely correct. Softupdates guarantees that you won't get > > > > corruption due to metadata pointing to invalid or stale data blocks. > > > > That's not the same as guaranteeing that there won't be any corruption. > > > > Write caching on the drive combined with an in-opportune power loss or > > > > other failure can easily leave you with corrupt or incomplete metadata > > > > and/or data blocks. A panic while metadata is being committed to disk can > > > > also leave the metadata highly inconsistent and prone to corruption. > > > > This isn't to say the SU is bad or that other strategies are necessarily > > > > better, just that there are definite risks. > > > > > > If you just want to generalize it, you can say that "SoftUpdates > > > guarantees that your file systems will not get corrupt due to just > > > software errors." I don't particularly think not having UPS is a > > > good idea, but those can fail, and even so the ordering is such > > > that a truncated inode won't result in a truly corrupt filesystem, > > > and the inode doesn't get written until its contents are written > > > out. > > > > > > Also, hw.ata.wc really shouldn't default to 1. > > > > > > > GAH! No, please don't start this war again! The last time that we tried > > turning this off in a release (4.1 IIRC), were were plagqued by months of > > earthquakes, plagues, and deaths of first-born youngsters. I 100% agree > > that write caching in ATA is not compatible with data integrety, but the > > ATA marketting machine has convinced us that cached+untagged speed is > > better than uncached+tagged safety. C'est la vie, or so they say here. > > I think it would be prudent to add a nice fat "WARNING:" printf to the > boot process. It's really not obvious that FreeBSD defaults to having > your hard drives run "unsafely," even though it is usually faster. -- ------------------------ - Software is like sex - - it's better when - - it's free - - Linus Torvalds - ------------------------
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