tip below…

On Nov 13, 2011, at 3:24 AM, Pasi Kärkkäinen wrote:

> On Sat, Nov 12, 2011 at 10:08:04AM -0800, Richard Elling wrote:
>> On Nov 12, 2011, at 8:31 AM, Pasi Kärkkäinen wrote:
>>> On Sat, Nov 12, 2011 at 08:15:31AM -0500, David Magda wrote:
>>>> On Nov 12, 2011, at 00:55, Richard Elling wrote:
>>>>> Better than ?
>>>>> If the disks advertise 512 bytes, the only way around it is with a 
>>>>> whitelist. I would
>>>>> be rather surprised if Oracle sells 4KB sector disks for Solaris systems?
>>>> Solaris 10. OpenSolaris.
>>>> But would it be surprising to use SANs with Solaris? Or perhaps run 
>>>> Solaris under some kind of virtualized environment where the virtual disk 
>>>> has a particular block size? Or maybe SSDs, which tend to 
>>>> read/write/delete in certain block sizes?
>>>> In these situations simply assuming 512 may slow things down.
>>>> And if Solaris 11 is going to be around for a decade or so, I'd hazard to 
>>>> guess that 512B sector disks will become less and less prevalent as time 
>>>> goes on. Might as well enable the functionality now, when 4K is rarer, so 
>>>> you have more time to test and tunes things out?rather than later when you 
>>>> can potentially be left scrambling.
>>>> As Pasi Kärkkäinen mentions, there's not much you can do if the disks lies 
>>>> (just as has been seen with disks that lie about flushing the cache). This 
>>>> is mostly a temporary kludge for legacy's sake. More and more disks will 
>>>> be truthful as times goes on.
>>> Most "4kB"/sector disks already today properly report both the physical 
>>> (4kB) and logical (512b) sector sizes.
>>> It sounds like *solaris is only checking the logical (512b) sector size, 
>>> not the physical (4kB) sector size..
>> ZFS uses the physical block size.
>> http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/fs/zfs/vdev_disk.c#294
> Hmm.. so everything should just work? 
> Does some other part of the code use logical block size then, for example to 
> calculate the ashift? 
> Maybe I should read the code :) 

Or look at what your system reports :-) Though not directly intended for this 
        echo ::sd_state | mdb -k
and look for the un_phy_blocksize.
 -- richard


ZFS and performance consulting
LISA '11, Boston, MA, December 4-9 

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