Linux-kernel mailing list archive 1998-31,: Re: IDE drive data transfer rates, kernel optimization?

# Re: IDE drive data transfer rates, kernel optimization?

Aaron Tiensivu (tiensivu@pilot.msu.edu)
Wed, 5 Aug 1998 17:59:13 -0400

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> I am concerned about the advertised data rates of IDE hard disks,
> more specifically the "true maximum throughput" of said drives.

No present drive seems to approach the 33 spec..

> I have a Quantum Fireball SE 4.3G drive that claims UDMA
> capability. I am getting 7.8Mb/s out of this drive. This is

I get ~9.5MB on an "old" IBM Deskstar 6.4GB UDMA on a non-UDMA (!) motherboard.
Once my UDMA-able motherboard comes, I hope the rates will rise but I have my
doubts. I'll be driving the drive at a 'sane' mhz instead of the current 41mhz
bus I'm driving it at.

> As you can see, it says "BuffSize=80kB". That is NOT 128k for
> sure.

It's probably dedicated part of the buffer to firmware is my guess on the
matter. Also, some drives report incorrectly (for some odd reason) the amount
of cache they really do have.

> This is NOT the rated 33megs per second that the sheet claims for
> UDMA operation. The rate for PIO/DMA is 16.6Mb/s. I get 7.8Mb/s
> or roughly half of spec. Does this mean that if I use UDMA, I
> can expect around double, or 15Mb/s? If so, that is far from
> 33Mb/s, and still not quite even the calculated 19.75Mb/s that
> the internal buffer supports.

Currently, the 33 is a marketing gimmick.. ATA66 is coming but I don't see
drives hitting that rate for a long while.

> /dev/hda:
> multcount = 16 (on)

If your drive can go higher, it is usually beneficial to push it above that.
More data per interrupt.

> unmaskirq = 0 (off)

You can usually get a performance boost by enabling it. I've only seen
DTC VLB I/O cards munge this up.

> using_dma = 0 (off)

This should be enabled.

> Now back to your regularly scheduled programming. (pun intended)

You can munge with the various -X settings but usually, drives default to their
optimal level..

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