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Theodore Ts'o wrote: > On Mon, Jun 27, 2005 at 03:18:30PM -0500, Steve Lord wrote: > >>I presume Ted is referring to problems guaranteeing the integrity of >>the journal at recovery time. I am coming into this without all the >>available context, so I may be barking up the wrong tree.... In >>particular, I am not sure how journaling whole blocks protects >>you from this. > > > Actually, I was talking about the problem what happens when power > fails while DMA'ing to the disk, and memory, which is more sensitive > to voltage drops than the rest of the system, starts sending garbage > to the bus, which the disk then faithfully writes to the inode table. > > As I recall, you were the one who told me about this problem, and how > it was fixed in Irix by using a powerfail interrupt to abort DMA > transfers, as well as giving me a program which tests for this > condition (basically it writes known test pattern to the disk, and > then you do an unclean shutdown, and you look to see if garbage is > written to the disk instead of one of the known test patterns). If it > wasn't you, it must have been Jim Mostek --- but I could have sworn it > was you..... > > - Ted > Your memory is better than mine, not sure about the test program, but there was at one point a scenario like that on Irix, and I quite probably did mention it to you. That was certainly not PC hardware, but more likely a large Irix system with multiple power busses spread around a large amount of hardware. I presume you are saying that the fact that ext3 journals complete inode blocks rather that subsections of inodes means that, should a similar trashing of metadata occur during power down, a journal replay would fix it? I see no way short of hardware fixes of avoiding the general problem of a system failing in an ugly manner like this. Unless you write everything to disk twice (i.e. journal all data), you can still end up with a legitimate set of metadata, and the master copy of your employee database full of nasty little bits of corruption. Steve - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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