From: Scott Merritt <Scsi@PragmaSoft.com>
To: David Anderson <david-anderson2003@mail.com>
Cc: linux-scsi@vger.kernel.org
Subject: Re: I/O Request [Elevator; Clustering; Scatter-Gather]
Date: Tue, 4 Mar 2003 09:14:51 -0500 [thread overview]
Message-ID: <20030304091451.1dc4c4ea.Scsi@PragmaSoft.com> (raw)
In-Reply-To: <20030304133201.18619.qmail@mail.com>
My understanding ... which may be misguided ...
Elevator: If three different users post read requests for Logical Block #1, #32678, and #4 respectively then it will be more efficient to sort the requests and process them in the sequence #1, #4, #32678 as it minimizes the disk seeking time/distance.
Clustering: "Combines multiple requests to adjecent blocks into a single request". I am not personally familiar with if/where this is done in the SCSI subsystem, but sounds vaguely reasonable (if you have already sorted requests for "Elevator").
Scatter/Gather: In my experience, this refers to the ability of a low level adapter to "gather" multiple pieces of a single disk request which are located in different (non-contiguous) areas of physical memory. This is typically done with some type of memory mapping or a direct memory access (DMA) mechanism that can sequence through a list of blocks. Intuitively, it would seem that Scatter/Gather capability would be required to effectively implement "Clustering".
Hope this helps.
Regards, Scott.
next prev parent reply other threads:[~2003-03-04 14:14 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-03-04 13:32 I/O Request [Elevator; Clustering; Scatter-Gather] David Anderson
2003-03-04 13:50 ` Jens Axboe
2003-03-04 21:10 ` Daniel Phillips
2003-03-04 14:20 ` Jens Axboe
2003-03-04 17:47 ` Bryan Henderson
2003-03-04 18:04 ` Luben Tuikov
2003-03-04 14:14 ` Scott Merritt [this message]
-- strict thread matches above, loose matches on Subject: below --
2003-03-04 14:11 David Anderson
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