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SubjectRe: writeback cache dangers Re: [ANNOUNCE] Ramback: faster than a speeding bullet
On Fri, Mar 14, 2008 at 08:03:57PM +0100, Pavel Machek wrote:
>
> > The ingest rate at the time of a power hit makes a huge
> > difference as well - basically, pulling the power cord
> > when a box is idle is normally not harmful. Try that
> > when you are really pounding on the disks and you will
> > see corruptions a plenty without barriers ;-)
>
> I tried that, and could not get a corrruption. cp -a on big kernel
> trees, on sata disk with writeback cache and no barriers... and I
> could not cause fs corruption. ext3.
>
> I'd like to demo danger of writeback cache. What should I do?

Ext3's journal probably hides a huge number of problems. I'd try
something with a lot more parallel modifications to metadata. Say
postmark with a large number of threads. It would be interesting
actually to get some controlled results of exactly how busy a
filesystem has to be before you get filesystem corruption (which I
would check explicitly running "e2fsck -f" e2fsck after pulling the
plug on the drive).

- Ted


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