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Re: [vox-tech] Raid 1 - Fresh Install - Drives seem slow
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Re: [vox-tech] Raid 1 - Fresh Install - Drives seem slow



> Thanks Bill, yep I know it will rebuild slowly in the background.  I 
> hadn't filled in the new info I have since no one had responded, and 
> figured the thread was dead.
> 
> Here's the deal
> 
> I just installed a simple raid-1.  I have a single HD on each 
> controller.  ie. 2 controllers 2 HDs. That's it, no CD players or DVD 
> drives...
> 
> I did a fresh install of Sarge.  After reboot I unplugged the CD drive, 
> and let the array sync overnight.  It took 10hrs to sync 160GiB, which 
> seemed pretty long, so I executed the "dd if=/dev/hda of=/dev/null 
> bs=64k count=10000" command I've seen posted on the raid list.

Sure, so you are reading 600 MB from /dev/hda

> It took about a minute and change to complete, which is long.  So out of 

So about 10MB/sec.

> curiosity I plugged in a CD player and booted Knoppix.  When I ran the 
> same command it took only 30 seconds (which is still not as quick as 
> some of the numbers on that list, but it's an old celeron 466MHz).

Right, 2.4 vs 2.6 kernels handle I/O differently, I don't consider dd
a very good measurement of performance since read/writes to raw
disk devices (without caches, buffering, ordering, or filesystem) are
pretty rare.

> So Knoppix is configuring something different, I'm searching for the 
> difference

I'd point at both the readahead and the large difference in kernel.

> I compared the result hdparm under both OSs
> Sarge:~# hdparm /dev/hda
> /dev/hda:
>  readahead    = 256 (on)
> 
> knoppix:~# hdparm /dev/hda
>  readahead    =  8 (on)
>  geometry     = 19457/255/63, sectors = 312581808, start = 0

> < Linux version 2.6.8-2-686 (dilinger@toaster.hq.voxel.net) (gcc version 
> ---
> > Linux version 2.4.27 (root@Koffer) (gcc version 2.95.4 20011002 

-- 
Bill Broadley
Computational Science and Engineering
UC Davis
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