New hard disk architectures

Keith wrote:
lid says...
Should the strategy or size change if the HD hw does more
layout-aware buffering?

What gain?

Extra track-to-track seeks: The OS has no idea of where the
actual track ends are (variable zones) due to remapping by the
HD controller. So when it does read-ahead, it may requires
an extra (potentially unneeded and expensive) track step.

It should be better than that, but it is still horrid
compared to a dedicated master.

You are right, it is slightly better than that (DWORD IO).
I with thinking of only byte-wise IO:

# hdparm -d 0 /dev/hda
/dev/hda: setting using_dma to 0 (off)
# hdparm -tT /dev/hda
Timing buffer-cache reads: 488 MB in 2.01 seconds = 242.46 MB/sec
Timing buffered disk reads: 14 MB in 3.43 seconds = 4.08 MB/sec

# hdparm -d 1 /dev/hda
/dev/hda: setting using_dma to 1 (on)
# hdparm -tT /dev/hda
Timing buffer-cache reads: 504 MB in 2.01 seconds = 250.29 MB/sec
Timing buffered disk reads: 60 MB in 3.02 seconds = 19.85 MB/sec


THe issue was interleaving though. While the DMA controller is
moving data the CPU can be figuring out what to do with it[*].

Or more likely, running other tasks/threads.

The bits streaming off the platter become the limiting factor.

And have been for quite some time (386?)

-- Robert

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In article ,
Jan Panteltje wrote:
On a sunny day (Wed, 28 Dec 2005 15:57:18 -0500) it happened Keith
wrote in :

In article ,
says...
On a sunny day (Tue, 27 Dec 2005 23:23:39 -0500) it happened Keith

$1
$2
$3
$4
$5

By my calculations, you owe me $15 for the education.
mm, try to think out of your box.
In politics if you 'owe' somebody, it could well be in the form of
nukes.

The '$' stands for paragraph.

I think this is the symbol you meant to use (hopefully it'll work):

¶

"$" is a currency symbol, not a paragraph marker.

_/_
/ v \ Scott Alfter (remove the obvious to send mail)
(IIGS( http://alfter.us/ Top-posting!
\_^_/ rm -rf /bin/laden What's the most annoying thing on Usenet?

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