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Date:	Sun, 20 Jul 2014 11:47:06 -0700
From:	"Linda A. Walsh" <lkml@...nx.org>
To:	Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Howto tell kernel to use 4096 as granularity & minimum size?

I have a hard disk with a "512e" sector size: emulated 512, really 4096.

The disk returns a 512-byte size to drivers for compatibility.

I can partition the disk and setup the allocation size
to 4096, but I'd like to tell the kernel to use a
virtual-size of 4096 for the sector as an additional
performance 'hint', so nothing will even try to use
smaller i/o's than that.

However, this doesn't seem to work ("# prompt" does mean root):

/sys/block/sdd/queue#   echo 4096 >minimum_io_size    
bash: minimum_io_size: Permission denied

I realize this is probably implemented as a R-O value,
but it there a reason it needs to be if an admin
wants to increase it to a multiple of an emulated
I/O size so as to have it represent the physical
sector size?

I.e. if the "/sys" code was patched to allow modification
of this variable, would it work for the purpose
I am describing (i.e. ignoring emulated 512 size and
using the real 4096 size as a minimum (I wouldn't
intend or want this to affect the sector# addressing,
which would still be done using 512B sector blocks.

Thanks!


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