On 23.07.2010 08:10, Stan Hoeppner wrote:
> Michael Monnerie put forth on 7/23/2010 5:59 AM:
> > On Freitag, 23. Juli 2010 Christoph Hellwig wrote:
> >> -b size=4096 is the default anyway, for 4k sector drivers you also
> >> want -s size=4096, which you do not want for 512 byte sector disks.
> > Thanks for clarification. Should I use "-s size=4096" despite the drive
> > saying 512b sectors? It's a "hidden" 4K sector drive, so maybe declaring
> > it extra for XFS helps performance? Or does it not matter at all?
> >> What values do the files
> >> /sys/block/<device>/queue/logical_block_size
> >> /sys/block/<device>/queue/physical_block_size
> >> /sys/block/<device>/alignment_offset
> >> say about your disk?
> > 512, 512, 0 for a Western Digital D20EARS-00MVWB0 (2TB) which has 4K
> > sectors but obviously hides it.
> The WD20EARS-00MVWB0 is definitely a 4k sector drive:
> If you're currently seeing somewhere between 60-120MB/s per drive with hdparm
> or dd then you don't need to further tweak anything. If alignment is off,
> from all I've read, performance will be abysmal, down in the sub 30MB/s range.
Only for writes, reads are for practically unaffected.
The problem for write is the "Read Modify Write" Cycle that is needed
when you don't change all 8 512byte "sub-"sectors contained in a 4096
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