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

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

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On Thu, 2005-06-23 at 09:03 -0400, Guy wrote:
> 
> > -----Original Message-----
> > From: Ming Zhang [mailto:mingz@ele.uri.edu]
> > Sent: Thursday, June 23, 2005 8:32 AM
> > To: Guy
> > Cc: bdameron@pivotlink.com; linux-raid@vger.kernel.org
> > Subject: RE: More tales of horror from the linux (HW) raid crypt
> > 
> > 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.
> But, this is hardware RAID.  A re-sync would not affect the PCI bus.  All
> disk i/o related to re-building the array would be internal to the card.
> However, even if it were a software RAID card, the PCI-X would be at 68.2%
> load, so it should not be a problem.  If my math is correct!  :)
> 
> Also, a single RAID5 array on 24 disks would be high risk of a double
> failure.  I think I would build 2 RAID5 arrays of 12 disks each.  Or 2 RAID5
> arrays of 11 disks each, with 2 spares.
> 
or build with raid6. but anyway, once u a disk, u will need to have a
rsync. with MD, u might try the fr5.

no money, otherwise buy one and try. :P

i think i need a 4U unit, dual amd64...

ming

> > 
> > >
> > > Guy
> > >
> > > >
> 
> 

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