Hard rive speed : raw vs formatted ?! :-(((

James Wilkinson ubuntu at westexe.demon.co.uk
Wed May 4 16:39:03 UTC 2005


Vincent Trouilliez wrote:
> I just replaced my main hard drive, with a brand new one.
> Using hdparm, it managed only about 17MB/s.
> "Out of the box" (unpartitioned), the new/replacement drive managed an
> amazing 60MB/s.
> I couldn't wait to transfer Ubuntu on it to see how much it would
> improve things. But, once the system was "cloned" on it, hdparm would
> only return about 27MB/s ... not even half the first reading !
> 
> What the hell happened to the drive  ? :o(
> I don't understand why would a partitioned and formatted disk be 50%
> slower than a "raw" disk ?! I feel like cheated on... :o(
> 
> I couldn't believe it. I thought that maybe the problem was that when I
> cloned the disk, it was plugged as single master on hdc, but once
> cloned, was being plugged a master, hda, but with a slave hard drive
> (which contains breezy) on hdb. I turned hdb off with hdparm prior to
> running the test on hda, but no luck.
> So I unplugged hdb altogether, to leave hda alone on the IDE bus, then
> ran the hdparm test again from a live CD, hoping for the best but....
> no, speed was still stuck to 30MB/s max !
> 
> I made sure that the "acoustic management" was set to "loud/fast", which
> it was.
> 
> So really, I can't see any explanation other than putting the
> partition/filesystem/data on the disk...and I still can't understand it
> would make any difference regarding the hdparm test.

Odd.

One thing to check: cables and DMA mode.

If you have an old 40 pin cable, then the disk / driver / adapter aren't
supposed to go any faster than 33 MB/s = udma2
Check with
hdparm -i /dev/hda

It's also possible that the old hard drive was only set for udma2 and
that got written somewhere into the configuration. When you cloned the
disk, that setting "stuck". A quick glance suggests that
/etc/hdparm.conf is the obvious place to stick such things, but I'm not
sufficiently used to Debian / Ubuntu to be sure. On my new install, the
only uncommented non-blank line is "quiet".

There is a chance that the live CD was being cautious with hardware it
wasn't sure about (you really don't want your filesystems fried, whether
by your main OS or a live CD). There's also a chance that the BIOS set
up both hard drives to udma2 (as the maximum they both support) because
it saw they were on the same channel, and I wouldn't be sure that Linux
would automatically speed the interface up.

In any case, checking with hdparm -i will tell you if it's the disk or
the interface, and give you somewhere else to look.

Hope this helps,

James.

-- 
E-mail address: james | "What kind of music do you get here, ma'am?"
@westexe.demon.co.uk  | "Why, we get both kinds of music, Country and
                      | Western."




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