Re: MD/RAID: what's wrong with sector 1953519935?

[Ric Wheeler]

On 08/25/2009 10:22 PM, Andrei Tanas wrote:
> > > > One thing that can happen is when we have a hot spot (like the super
> > > > block) on high capacity drives is that the frequent write degrade
> > the
> > > > data in adjacent tracks.  Some drives have firmware that watches for
> > > > this and rewrites adjacent tracks, but it is also a good idea to
> > avoid
> > > > too frequent updates.
> > >
> > > Yet another detail to worry about.... :-(
> >
> > it never ends :-)
> >
> > > > Didn't you have a tunable to decrease this update frequency?
> > >
> > > /sys/block/mdX/md/safe_mode_delay
> > > is a time in seconds (Default 0.200) between when the last write to
> > > the array completes and when the superblock is marked as clean.
> > > Depending on the actual rate of writes to the array, the superblock
> > > can be updated as much as twice in this time (once to mark dirty,
> > > once to mark clean).
> > >
> > > Increasing the number can decrease the update frequency of the
> > superblock,
> > > but the exact effect on update frequency is very load-dependant.
> > >
> > > Obviously a write-intent-bitmap, which is rarely more that a few
> > > sectors, can also see lots of updates, and it is harder to tune
> > > that (you have to set things up when you create the bitmap).
> > >
> > > NeilBrown
> >
> > We did see issues in practice with adjacent sectors with some drives,
> > so this
> > one is worth tuning down.
> >
> > I would suggest that Andrei might try to write and clear the IO error
> > at that
> > offset. You can use Mark Lord's hdparm to clear a specific sector or
> > just do the
> > math (carefully!) and dd over it. It the write succeeds (without
> > bumping your
> > remapped sectors count) this is a likely match to this problem,
>
> I've tried dd multiple times, it always succeeds, and the relocated sector
> count is currently 1 on this drive, even though this particular fault
> happened at least 3 times so far.

I would bump that count way up (say to 2) and see if you have an issue...

ric

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/