linux-kernel - absurdly high "optimal_io

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Message-ID: <545BA625.40308@windriver.com>
Date:	Thu, 6 Nov 2014 10:47:33 -0600
From:	Chris Friesen <chris.friesen@...driver.com>
To:	Jens Axboe <axboe@...nel.dk>, lkml <linux-kernel@...r.kernel.org>
Subject: absurdly high "optimal_io_size" on Seagate SAS disk

Hi,

I'm running a modified 3.4-stable on relatively recent X86 server-class 
hardware.

I recently installed a Seagate ST900MM0026 (900GB 2.5in 10K SAS drive) 
and it's reporting a value of 4294966784 for optimal_io_size.  The other 
parameters look normal though:

/sys/block/sda/queue/hw_sector_size:512
/sys/block/sda/queue/logical_block_size:512
/sys/block/sda/queue/max_segment_size:65536
/sys/block/sda/queue/minimum_io_size:512
/sys/block/sda/queue/optimal_io_size:4294966784

The other drives in the system look more like what I'd expect:

/sys/block/sdb/queue/hw_sector_size:512
/sys/block/sdb/queue/logical_block_size:512
/sys/block/sdb/queue/max_segment_size:65536
/sys/block/sdb/queue/minimum_io_size:4096
/sys/block/sdb/queue/optimal_io_size:0
/sys/block/sdb/queue/physical_block_size:4096

/sys/block/sdc/queue/hw_sector_size:512
/sys/block/sdc/queue/logical_block_size:512
/sys/block/sdc/queue/max_segment_size:65536
/sys/block/sdc/queue/minimum_io_size:4096
/sys/block/sdc/queue/optimal_io_size:0
/sys/block/sdc/queue/physical_block_size:4096

According to the manual, the ST900MM0026 has a 512 byte physical sector 
size.

Is this a drive firmware bug?  Or a bug in the SAS driver?  Or is there 
a valid reason for a single drive to report such a huge value?

Would it make sense for the kernel to do some sort of sanity checking on 
this value?

Chris
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