On Sat, 25 Oct 2003, James Moe wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On Sun, 26 Oct 2003 16:24:17 +1300, Mark Kirkwood wrote: > > >I would conclude that it not *always* the case that power failure > >renders the database unuseable. > > > >I have just noticed a similar posting from Scott were he finds the cache > >enabled case has a dead database after power failure. > > > Other posts have noted that SCSI never fails under this condition. Apparently SCSI > drives sense an impending power loss and flush the cache before power completely > disappears. Speed *and* reliability. Hm.
Actually, it would appear that the SCSI drives simply don't lie about fsync. I.e. when they tell the OS that they wrote the data, they wrote the data. Some of them may have caching flushing with lying about fsync built in, but the performance looks more like just good fsyncing to me. It's all a guess without examining the microcode though... :-) > Of course, anyone serious about a server would have it backed up with a UPS and > appropriate software to shut the system down during an extended power outage. This > just > leaves people tripping over the power cords or maliciously pulling the plugs. Or a CPU frying, or a power supply dying, or a motherboard failure, or a kernel panic, or any number of other possibilities. Admittedly, the first line of defense is always good backups, but it's nice knowing that if one of my CPUs fry, I can pull it, put in the terminator / replacement, and my whole machine will likely come back up. But anyone serious about a server will also likely be running on SCSI as well as on a UPS. We use a hosting center with 3 UPS and a Diesel generator, and we still managed to lose power about a year ago when one UPS went haywire, browned out the circuits of the other two, and the diesel generator's switch burnt out. Millions of dollars worth of UPS / high reliability equipment, and a $50 switch brought it all down. ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
