Re: no merit from using DMA-66?

[Vachirasuk <vachi@pop07.odn.ne.jp>]

Hi,

From: "Stephan Hachinger" <Stephan.Hachinger@gmx.de>
Subject: Re: no merit from using DMA-66?
Date: Sun, 19 Mar 2000 22:06:49 +0100

> Hello!
> 
> That has something to do with your hard disk cache. Because, when the data
> requested by the PC happens to be in the internal cache (typically
> 512k-2megs), it can be transferrred to the mainboard at full bus speed rate!
> That's an improvement of UDMA! And, the interfaces are always a little bit
> faster, then the disks are getting faster, and then they make a new
> interface standard again. That's how it always is, because, it is better to
> not to have problems with a slow interface.

Thanks for the explanation. I really learn something here :-)

> So, either your benchmark doesn't manage to switch off the cache for its
> measure or it only shows you the highest bus speed rate. But, 33MB/66MB is
> definitely not a data rate any recent IDE HDD can achieve.

I have tried asking around on japanese debian-user list and there is a
person said he got 25MB/sec DTR on IBM harddisk from the test with
hdparm. Moreover from hdparm manpage about -t option:
              This  displays  the  speed  of  reading through the
              buffer cache to the disk without any prior  caching
              of  data.  This measurement is an indication of how
              fast the drive can sustain  sequential  data  reads
so I guess the DTR is measured with the cache on. This should give
some better DTR over DMA-33 harddisk, if I got it right? 

Best regards,

Vachi

-----
Vachirasuk Setalaphruk
ISE, Osaka University