Re: FFSv1 performance on large filesystems

Matthias Scheler writes:
> On Wed, Mar 23, 2005 at 07:13:49PM -0600, Greg Oster wrote:
> > > No, it's RAID-1. But writes should still happen in parallel there.
> > They do.
> 
> RAIDframe queues them in parallel. But maybe something in the kernel
> searilizes them?

Shouldn't be...

For kicks:  Try your "single disk" benchmark on the two disks at the same 
time... 

Also: do both disks bench out at the same rate?  RAID-1 will be 
limited by the slower of the two.

> > What does your raid0.conf file look like?
> 
> The RAID gets autoconfigured. But the configuration file I used for
> creating it looked like this:
> 
> START array
> 1 2 0
> START disks
> /dev/wd0a
> /dev/wd1a
> START layout
> 128 1 1 1
> START queue
> fifo 100

Looks fine/normal.

> > I'd expect a RAID 1 set to write a little slower than the raw disk,
> > but not this much slower.
> 
> Yes, me too. It should be slower by the latency it takes to deliver the
> write to the second disk. But not by a factor of two.

It should just be slower by the amount of time it takes to make sure 
the drives claim the writes complete before reporting that a given 
write is done...

What do your disklabels look like for the RAID set and for the 
'single disk' test case?

> > I'd also be interested in ccd(4) results (with the same stripe 
> > widths...)
> 
> It's not a stripe it's a mirror.

Oh.. right.. you said that, and I knew that.. *blush*  (I had "ccd on 
the brain" from thorpej's earlier comments :-} )

Later...

Greg Oster