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From: Tim Walker <tim.t.walker@seagate.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Phillip Susi <phill@thesusis.net>,
	Damien Le Moal <damien.lemoal@wdc.com>,
	Jens Axboe <axboe@kernel.dk>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>
Subject: Re: [PATCH v6 0/5] Initial support for multi-actuator HDDs
Date: Fri, 27 Aug 2021 17:00:25 +0000	[thread overview]
Message-ID: <D2424B1B-8EAC-4A12-B92B-B469DA38E3A7@seagate.com> (raw)
In-Reply-To: <YSkVwSfQ/9RCKfEG@infradead.org>


On  Friday, August 27, 2021 at 12:42:54 PM Christoph Hellwig wrote:
>
>
>
>On Fri, Aug 27, 2021 at 02:28:58PM +0000, Tim Walker wrote:
>> There is nothing in the spec that requires the ranges to be contiguous
>> or non-overlapping.
>
>Yikes, that is a pretty stupid standard.  Almost as bad as allowing
>non-uniform sized non-power of two sized zones :)
>
>> It's easy to imagine a HDD architecture that allows multiple heads to access the same sectors on the disk. It's also easy to imagine a workload scenario where parallel access to the same disk could be useful. (Think of a typical storage design that sequentially writes new user data gradually filling the disk, while simultaneously supporting random user reads over the written data.)
>
>But for those drivers you do not actually need this scheme at all.
>Storage devices that support higher concurrency are bog standard with
>SSDs and if you want to go back storage arrays.  The only interesting
>case is when these ranges are separate so that the access can be carved
>up based on the boundary.  Now I don't want to give people ideas with
>overlapping but not identical, which would be just horrible.
>

Christoph - you are right. The main purpose, AFAIC, is to expose the parallel access capabilities within a LUN/SATA target due to multiple actuators. I hope the ranges are *always* contiguous and *never* overlapping.  But there's no telling what somebody has up their sleeve. 

Best regards,
-Tim


  reply	other threads:[~2021-08-27 17:00 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-27  7:50 [PATCH v6 0/5] Initial support for multi-actuator HDDs Damien Le Moal
2021-08-27  7:50 ` [PATCH v6 1/5] block: Add independent access ranges support Damien Le Moal
2021-08-27  7:50 ` [PATCH v6 2/5] scsi: sd: add concurrent positioning " Damien Le Moal
2021-08-27  7:50 ` [PATCH v6 3/5] libata: support concurrent positioning ranges log Damien Le Moal
2021-08-27  7:50 ` [PATCH v6 4/5] doc: document sysfs queue/independent_access_ranges attributes Damien Le Moal
2021-08-27  7:50 ` [PATCH v6 5/5] doc: Fix typo in request queue sysfs documentation Damien Le Moal
2021-08-27 13:58 ` [PATCH v6 0/5] Initial support for multi-actuator HDDs Phillip Susi
2021-08-27 14:28   ` Tim Walker
2021-08-27 16:41     ` Christoph Hellwig
2021-08-27 17:00       ` Tim Walker [this message]
2021-08-29 22:55       ` Damien Le Moal
2021-08-27 17:34     ` Phillip Susi
2021-08-29 22:50       ` Damien Le Moal

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