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?
