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Re: Direct I/O question: How to get dioinfo using ioctl?

To: "Rosenthal, Eric S." <Eric.S.Rosenthal@xxxxxxxxxx>
Subject: Re: Direct I/O question: How to get dioinfo using ioctl?
From: Rajagopal Ananthanarayanan <ananth@xxxxxxx>
Date: Mon, 14 May 2001 16:38:24 -0700
Cc: "'linux-xfs@xxxxxxxxxxx'" <linux-xfs@xxxxxxxxxxx>
References: <99A560B38BC6D21180020004ACA6B36A031FAF65@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
"Rosenthal, Eric S." wrote:
> 
        [ ... ]
> 
> As for the fact that direct I/O is slower than buffered I/O - we're
> running version 2.4.2 of the Kernel on a PC, and have 2 striped hard drives
> connected with a Scsi controller (we plan to add more drives).  The disks
> are striped at 4K and the file system block size is 4K.  I'll have to do
> some tests to see which sizes are optimal.
> 
> The disk rate I got for direct I/O (25 MB/sec) is about what was expected
> but the rate with buffered I/O (27 MB/sec with the cache cleared) is higher
> than I would've throught.  Could Linux just handle buffered I/O better than
> Irix/NT?


By I/O do you mean read, write or both? For streaming buffered
writes XFS will do nearly as good as raw I/O on the machines I've
tested (scsi disk) ... I can't readily account for better
buffered read performance.

ananth.

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Rajagopal Ananthanarayanan ("ananth")
Member Technical Staff, SGI.
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