Messages in this thread | | | Date | Thu, 17 Jan 2008 18:18:05 -0500 | From | Ric Wheeler <> | Subject | Re: [Patch] document ext3 requirements (was Re: [RFD] Incremental fsck) |
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Theodore Tso wrote: > On Wed, Jan 16, 2008 at 09:02:50PM -0500, Daniel Phillips wrote: >> Have you observed that in the wild? A former engineer of a disk drive >> company suggests to me that the capacitors on the board provide enough >> power to complete the last sector, even to park the head. >>
Even if true (which I doubt), this is not implemented.
A modern drive can have 16-32 MB of write cache. Worst case, those sectors are not sequential which implies lots of head movement.
> > The problem isn't with the disk drive; it's from the DRAM, which tend > to be much more voltage sensitive than the hard drives --- so it's > quite likely that you could end up DMA'ing garbage from the memory. > In fact the fact that the disk drives lasts longer due to capacitors > on the board, rotational inertia of the platters, etc., is part of the > problem.
I can tell you directly that when you drop power to a drive, you will lose write cache data if the write cache is enabled. With barriers enabled, our testing shows that file systems survive power failures which routinely caused corruption without them ;-)
ric
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