Greg Freemyer schrieb:
"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.
Just a guess, but I would bet you have some sector remapping going on
in the early portion of the 10/MB/sec drive.
Thus once dd gets based the area that has remapped sectors, it speeds up.
When reading the slow LBA sectors, the head is actually having to seek
back and forth from the primary sector area out to the spares area.
I've seen that before.
There is some logic in this, but:
- smartctl doesn't show any remappings - AFAIK it should?
- there are some more of these HP ProLiant BL30p G1 blades here - some
show this behaviour, some don't (i.e., both drives are as fast from the
very beginning). Always the first drive shows this behaviour.
Could be an issue with these WDC WD2500BEVE-00WZT0 drives when they are
connected as master? Why the issue doesn't show up on all such blades?
FYI: I saw a drive last week that had over 10% of the first 200
sectors bad. After that all was good. The drive I was looking at was
several years old and remapping had not been triggered, so it was
obvious what was going on when I ran dd to try and read the entire
drive.
--
Tomasz Chmielewski
http://wpkg.org
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