linux-kernel - Re: [PATCH 07/14] target/sbc: Add P_TYPE + PROT_EN bits to READ_CAPACITY

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Message-ID: <yq1eh4fr2ee.fsf@sermon.lab.mkp.net>
Date:	Fri, 10 Jan 2014 15:46:17 -0500
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Andy Grover <agrover@...hat.com>
Cc:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	Sagi Grimberg <sagig@...lanox.com>,
	"Nicholas A. Bellinger" <nab@...erainc.com>,
	target-devel <target-devel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Christoph Hellwig <hch@....de>, Hannes Reinecke <hare@...e.de>,
	Or Gerlitz <ogerlitz@...lanox.com>
Subject: Re: [PATCH 07/14] target/sbc: Add P_TYPE + PROT_EN bits to READ_CAPACITY_16

>>>>> "Andy" == Andy Grover <agrover@...hat.com> writes:

Andy> Yes, don't you need FORMAT UNIT because protection information is
Andy> going to mean the pi-enabled lun will need to report less blocks?

Modern disk drives won't shrink when you reformat them with PI. This is
a result of an IDEMA agreement about LBA counts.

And if you create a 10GB PI LUN on an array you'll get 10GB for data.

Andy> The ramdisk backstore changes in this series allocate extra space
Andy> for PI info, but my understanding was that especially for
Andy> emulation with block and fileio backstores, everything needs to go
Andy> in the same amount of space.

For both file and block I'd recommend we store the PI in a separate
block device or file unless the backing device is PI-capable.

Andy> Furthermore, if we want PI info stored along with the blocks, then
Andy> block and fileio backstore formats are no longer going to be 1:1
Andy> -- requiring offset calculations, non-aligned read-modify-write,
Andy> and all that unpleasantness to be handled?

I only think interleaved makes sense if you're passing the PI through
instead of emulating.

-- 
Martin K. Petersen	Oracle Linux Engineering
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