RE: More tales of horror from the linux (HW) raid crypt

[Ming Zhang <mingz@ele.uri.edu>]

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On Wed, 2005-06-22 at 23:05 -0400, Guy wrote:
> > -----Original Message-----
> > >
> > > > will this 24 port card itself will be a bottleneck?
> > > >
> > > > ming
> > >
> > > Since the card is PCI-X the only bottleneck on it might be the Processor
> > since
> > > it is shared with all 24 ports. But I do not know for sure without
> > testing it.
> > > I personally am going to stick with the new 16 port version. Which is a
> > PCI-
> > > Express card and has twice the CPU power. Since there are so many
> > spindles it
> > > should be pretty darn fast. And remember that even tho the drives are
> > 150MBps
> > > they realistically only do about 25-30MBps.
> > 
> > the problem here is taht each HD can stably deliver 25-30MBps while the
> > PCI-x will not arrive that high if have 16 or 24 ports. i do not have a
> > chance to try out though. those bus at most arrive 70-80% the claimed
> > peak # :P
> 
> Maybe my math is wrong...
> But 24 disks at 30 MB/s is 720 MB/s, that is about 68.2% of the PCI-X
> bandwidth of 1056 MB/s.
yes, u math is better.

> 
> Also, 30 MB/s assumes sequential disk access.  That does not occur in the
> real world.  Only during testing.  IMO
yes, only during test. but what if people build raid5 base on it, this
is probably what people do. and then a disk fail? then a full disk
sequential access becomes normal. and disk fail in 24 disk is not so
uncommon.

> 
> Guy
> 
> > 


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