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Re: Problem identified: WAPL/RAIDframe performance problems

On Fri, Nov 30, 2012 at 12:00:52PM +0000, David Laight wrote:
> On Fri, Nov 30, 2012 at 08:00:51AM +0000, Michael van Elst wrote:
> > (David Laight) writes:
> > 
> > >I must look at how to determine that disks have 4k sectors and to
> > >ensure filesystesm have 4k fragments - regardless of the fs size.
> > 
> > newfs should already ensure that fragment >= sector.
> These disks lie about their actual sector size.
> The disk's own software does RMW cycles for 512 byte writes.

These disks just follow their specification. They also report
the true sector size. The problem is how to interpret it, obviously
you can access the disk in 512 byte units and the real size and
alignment just affects performance. So should the disk lie about
the blocks you can address or lie about some recommended block size
for accesses?

The rest of the world just ignores such problems by using some
values that are sufficiently sized/aligned for old and new disks.

                                Michael van Elst
                                "A potential Snark may lurk in every tree."

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