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Date: Wed, 16 Mar 2011 18:11:49 -0500
From: Les Mikesell <lesmikesell@gmail.com>
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Subject: Re: [linux-lvm] Advanced Format disks mixed with regular disks?
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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.

-- 
   Les Mikesell
    lesmikesell@gmail.com