Re: reiser4 plugins

[Hans Reiser]

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
>
>
>  
>
Maybe a more positive approach would be to say, hey, I got this program
from the XFS guys that tests for DMA problems on power failure, maybe
all the Linux filesystem developers should give it a try?

Shall we try that style of interaction?

Ted, if this corruption hits an ext3 directory structure, and that
corrupted directory structure commits, what happens?  With ReiserFS
(Chris please comment here) it would have to corrupt the directory in
the journal, return successful IO, then after that point not corrupt the
commit block and have enough power to write the commit block.  How is
that different for XFS or ext3?

Hans
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