On Wed, 2004-06-02 at 17:07, Frank Smith wrote:

> If it's linux, try using hdparm to verify the modes and speed of your
> disk.  Like Jon says, a good drive can have terrible performance if
> it is running in the wrong mode.

hdparm is a nifty addition to my system monitoring toolkit (top, gnome's
cpu monitor icon, sticking my ear close to a drive to listen for seeks,
eyeballing the disk activity LED, and dump's data transfer messages).

hdparm uncovered some interesting information. The 2 drives on this
machine are identical and identically configured, except for one thing:
both are using dma, but one of them, hda, is udma2 and hdc is udma5. I
did a 'hdparm -X 69 /dev/hda' to set hda to udma5. hdparm said it did,
but hdparm -i still said udma2.

Jon implied that hdparm may be just kidding about this. hdparm -Tt gives
the following:

----
/dev/hda:
 Timing buffer-cache reads:   2800 MB in  2.00 seconds = 1399.51 MB/sec
 Timing buffered disk reads:   82 MB in  3.00 seconds =  27.33 MB/sec
 
/dev/hdc:
 Timing buffer-cache reads:   2772 MB in  2.00 seconds = 1386.21 MB/sec
 Timing buffered disk reads:  114 MB in  3.03 seconds =  37.62 MB/sec
----

Since I have no feel for what pio would be like, I don't know. But the
difference looks ballpark right for the different dma modes.

I looked at another system: an old Dell server downstairs with a Maxtor
PCI IDE card and a 2 or 3 year old Maxtor 60GB disk, also claiming to be
udma5:

---- 
/dev/hde:
 Timing buffer-cache reads:   128 MB in  0.59 seconds =216.95 MB/sec
 Timing buffered disk reads:  64 MB in  1.59 seconds = 40.25 MB/sec
---- 

Something is wrong here. The disks up here are much newer, and a lot
slower. I'm using the onboard controllers in an Intel D865GLC
motherboard. 

>    Also, make sure your kernel is using the correct chipset driver
> for your IDE controller.  On a machine at home I replaced the
> motherboard and my disk speeds dropped to under 2MB/sec.  I finally
> figured out that since I had a different controller than the one I had
> compiled in support for, the kernel had dropeed back to generic IDE
> support.  Rebuilding the kernel with the proper driver made an over 10X
> performance boost.

That's where I'm going next. Kernel dox, motherboard dox, Gentoo dox,
and hdparm's man page. And google, of course...

Does anyone know of an equivalent to hdparm -Tt for SCSI disks?
-- 
Glenn English <ghe AT slsware DOT com>