Re: strange performance of raid0

["Keld Jørn Simonsen" <keld@dkuug.dk>]

On Sun, Feb 15, 2004 at 01:05:25PM +0100, Keld Jørn Simonsen wrote:
> On Sun, Feb 15, 2004 at 01:54:11AM -0800, Matt Thrailkill wrote:
> > The you don't get as good performance because hdc1 is slow enough to
> > really drag it down.  Think about it, if reads are all going about
> > sequentially, it has to spend alot of time waiting on that 16mb/s drive
> > compared to the others.
> 
> I would have thought the disks would have worked towards gaining
> performance enhancements in some cumulative way, is that not so, in theory?
> 
> So why is 3 disks slower than 2?
> 
> > You probably can't get 100mb/s with the two because that would be pretty
> > efficient, and there's probably more overhead than that.
> > 
> > Shouldn't the 80gb drive be going faster than 16mb/s though?  Have you
> > checked hdparm to make sure dma and all the goodies are turned on for
> > it?
> 
> I have a 40 GB segate disk also, on the same motherboard IDE
> controller, it runs about 40 MB/s. So yes, the hdc1
> should go faster, and I have measured something like 40 MB/s
> on it in idler times. I think it is because it is running other 
> processes. The machine is a ftp mirror and the disk has RedHat
> and Fedora ISO images, so it is quite popular.

Hmm, I have ext3 filesystems, and they are updating the atime in the
inodes. Could that be it? inode flushing obstructing the striping?

Best regards
Keld
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