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Re: [linux-lvm] Advanced Format disks mixed with regular disks?



On Wed, Mar 16 2011 at  8:02pm -0400,
Mike Snitzer <snitzer redhat com> wrote:

> On Wed, Mar 16 2011 at  7:11pm -0400,
> Les Mikesell <lesmikesell gmail com> wrote:
> 
> > On 3/16/2011 5:55 PM, Mike Snitzer wrote:
> > >
> > >>On 3/14/2011 1:17 PM, Mike Snitzer wrote:
> > >>>Both LVM2 and Device Mapper have been updated to accommodate stacking
> > >>>such a mix of drives.
> > >>>
> > >>>See this for a bit more detail:
> > >>>http://people.redhat.com/msnitzer/docs/io-limits.txt
> > >>>
> > >>>Particularly, the "Stacking I/O Limits" section.
> > >>>
> > >>>The concern raised for partial (4k) writes to the 512b drive was
> > >>>discussed a bit more here: http://lkml.org/lkml/2010/2/22/295
> > >>
> > >>Unfortunately this does not help with the WD EARS model drives ( are
> > >>there any other 4kb sector drives on the market now? ), since they lie
> > >>and report that they have 512 byte sectors.
> > >
> > >I'm not following what you're saying.  The kernel's blk_stack_limits()
> > >infrastructure accounts for "desktop" class 4K devices too (4K physical,
> > >512b logical) -- as does DM and lvm2.
> > >
> > >If given:
> > >
> > >"desktop" class drive:
> > >physical_block_size=4096
> > >logical_block_size=512
> > >minimum_io_size=4096
> > >optimal_io_size=0
> > 
> > How does the kernel know about the physical_block_size when the
> > device reports itself as 512?  And they handle 512 byte writes, just
> > very slowly.
> 
> The drive exports the information as part of its response to the
> IDENTIFY DEVICE (for ATA) or READ CAPACITY (for SCSI) command -- it
> splits out the physical and logical block sizes along with other
> attributes.  The kernel's SCSI (and libata) layer issues these commands
> to the drive.

I just got Phillips' mail that the drive lies and reports 512/512.
(and I read your mail too quickly).

So yeah, the WD EARS drives are scary.  Best for WD to defend or explain
them.

Mike


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