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Date: Tue, 10 Apr 2012 13:28:28 -0400 From: Vivek Goyal <vgoyal@...hat.com> To: Mike Snitzer <snitzer@...hat.com> Cc: Jens Axboe <axboe@...nel.dk>, linux kernel mailing list <linux-kernel@...r.kernel.org>, martin.petersen@...cle.com Subject: Re: [RFC PATCH] block: Change default IO scheduler to deadline except SATA On Tue, Apr 10, 2012 at 12:13:07PM -0400, Mike Snitzer wrote: [..] > > So we are back to the question of can scsi devices find out if a Lun > > is backed by single disk or multiple disks. > > I'm not aware of any discrete attribute (comparable to 'rotational' > flag) that SCSI devices will advertise that indicates "I'm a raid > array". > > That said, we can have a _very_ good hint that a SCSI device is a raid array if: > > 1) optimal_io_size is not zero, minimum_io_size is not equal to > optimal_io_size, and optimal_io_size is a multiple of minimum_io_size > > 2) WCE=0 (higher-end arrays with a writeback cache) > > Determining 1 could be enough, we should probably ignore 2 as it isn't > an absolute indication that a device is composed of multiple devices > (especially not if considered independently of 1). Umm..., somehow relying on optimal_io_size != minimum_io_size sounds odd to me (assuming it works). I checked bunch of Luns exported to me and all of them have optimal_io_size=0. I have few FC Luns exported from two array vendors. I have few iscsi Luns exported from two separate vendors and all these luns have optimal_io_size=0. Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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