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



On Wed, Mar 16 2011 at  4:45pm -0400,
Phillip Susi <psusi cfl rr com> 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

conventional 512 drive:
physical_block_size=512
logical_block_size=512
minimum_io_size=512
optimal_io_size=0

Stacking these drives would result in a logical device that has:

physical_block_size=4096
logical_block_size=512
minimum_io_size=4096
optimal_io_size=0

And yes, there are native 4K "enterprise" class drives (4K physical, 4K
logical) in the market.

Mike


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