[plug] 2.4.24 mremap root exploit

[Bernd Felsche]

On Thu, Feb 19, 2004 at 07:38:30AM +0800, Craig Ringer wrote:
> On Thu, 2004-02-19 at 07:31, Craig Ringer wrote:

> > I'm currently playing with Bonnie++ to see what thrashing the system
> > turns up. As it's running live services, the benchmarks won't be fair,
> > but should be somewhat informative nonetheless.
> 
> *gack*

> I had to abort the Bonnie++ run on the RAID 5 array, because the system
> was crawling to a halt. Load avg >15, ls blocking for 30 seconds, etc.
> Bad stuff.

RAID5 + lots of writes == BAD on all systems.

No matter how good the operating system, RAID5 sustained-write
performance is best rated in nanopascals; it sucks. A write has in
effect to be replicated across all members of the array; so
tripling/quadruling/quintupling/... disk activity is expected.

Bonnie++ will likely cause any RAID5 system to resemble
inter-galactic void.

Some RAID5 systems put a large, non-volatile cache in the system so
that the host can go away with the delusion that all writes have
actually happened. That is IMO; bad. One of my customers lost half a
day's transactions because the disk controller received a reset when
a hot-plug drive was replaced - cache was emptied and writes were
"forgotten" resulting in a corrupted database.

> Something is clearly not right here. Whether it's
> LVM2/device-mapper (if so, LVM1 had the same problem), the kernel
> I/O scheduler, the 3ware driver, the 3ware card firmware, or
> something else I do not know.  Suggestions appreciated.

-- 
/"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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