On Mon, Feb 23, 2009 at 3:37 PM, Tomasz Chmielewski <mangoo@xxxxxxxx> 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? 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. 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. Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
