Tomasz Chmielewski wrote:
I have a ProLiant BL30p G1 machine running Debian Lenny (2.6.26 kernel).
It also has two identical, 2.5 inch WDC WD2500BEVE-00WZT0 IDE drives
(new drives, no smart/badblock errors). Both drives are connected to a
single IDE channel this machine has.
"hdparm -t" gives me different results for these drives: ~10 MB/s for
hda, and ~20 MB/s for hdb with "serverworks" driver on Debian's 2.6.26
kernel.
When using "pata-serverworks" with 2.6.28.7 kernel, hdparm shows the
same results (~10 MB/s for sda, ~20 MB/s for sdb).
However, when I run "dd if=/dev/sda of=/dev/null bs=64k", I can see with
iostat that for the first 7-8 seconds, reads are with ~10 MB/s speed.
Then, reads from sda are with ~20 MB/s or more and are on par with sdb.
Similar dd test for sdb shows that it delivers with speed of ~20 MB/s
from the first second.
Is there an explanation for that?
..
Well, as you have shown, both hdparm and dd give the same results
when doing (almost) the same test: the first 3 seconds are slow.
After that, I would assume that the kernel read-ahead algorithms
kick in better and improve things.
But 10-20Mbytes/sec is slow for most modern drives,
even for 2.5" drives. Older ones, sure, that's fine,
but the newest 2.5" drives should score between 40
and 100Mbytes/sec.
The drive you listed is a WD 250GB mobile drive, PATA interface.
I have a very similar WD drive here (WD2500BEAS) that regularly
tops 60Mbytes/sec with "hdparm -t".
The difference could easily be in the chipset used to communicate
with the drive. You said "serverworks" driver, and "pata-serverworks".
The kernel start up logs will have more information,
including the timing info chosen by libata.
Cheers
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