Hardware Striping

[Kenneth D. Merry]

On Thu, Apr 22, 2004 at 22:28:06 +0200, Jens Schweikhardt wrote:
> Ken et al,
> 
> On Wed, Apr 21, 2004 at 03:02:10PM -0600, Kenneth D. Merry wrote:
> # On Wed, Apr 21, 2004 at 22:44:09 +0200, Jens Schweikhardt wrote:
> # > hello, world\n
> # > 
> # > I want to change my system to no longer use vinum for striping, but
> # > rather a hardware solution. I do not intend to use mirroring or any
> # > other RAIDn>0 functionality. I have two pairs of identical U160 SCSI
> # > disks (2 Fujitsu MAN and MAM with 36GB each) where I want to build two
> # > mirrors, one from the MANs, and one from the MAMs. You get the idea.
> # > 
> # > Until now I'm using an Adaptec 29160 Host Adapter, but of course it is
> # > not HW-RAID0 capable. What card am I looking for?
> # 
> # The only reason to go with a hardware controller for RAID-0 is if you want
> # to boot from the array.
> 
> Yes, that's one of the reasons, plus certain issues with vinum.

Understandable.

> # Otherwise, you'll get better performance by using a software RAID-0
> # solution.  Going through a RAID stack and a SCSI layer on a RAID card with
> # a comparatively slow processor will generally be slower than using your
> # much faster host processor to do all of that.
> # 
> # ccd is an alternative if you don't want to use vinum.
> 
> I also want to get rid of a lot of configuration and any possible
> (present and future) maintenance issues that vinum and ccd have, like
> GEOMification and End-Of-Life. I do not want to make any assumptions
> about them, and the proper way to get rid of that issue is to simply not
> use them. Call me paranoid :-)

That's understandable as well.

> # > The disks have a sustained read rate of 60 to 70 Mbyte/s, so if all of
> # > them were used at the same time they could saturate an U160 bus. Is this
> # > a problem?
> # 
> # It's not a problem, unless you're interested in performance.  I'd suggest a
> # 2 channel Ultra160 or Ultra320 RAID controller.  Hopefully the processor on
> # the RAID controller will be able to keep up with the 280MB/sec theoretical
> # maximum bandwidth from those disks.
> # 
> # As for alternatives, you could get an Adaptec 2200S, or an LSI MegaRAID
> # SCSI 320-2.  I think the driver for the Adaptec is probably a little better
> # maintained at the moment.  I haven't used either card, though, so I can't
> # really comment on them more than to point out the alternatives.
> 
> I've looked at other Adaptec products, and found
> 
>  29320-R := single channel U320 RAID0,1   Part Number: 1978100
> 
> which appears close to what I want, namely not the fully fledged RAID>1,
> and as a benefit there is an 68 pin Ultra Wide connector for my CD
> writer and DVD reader, so all my present devices can be used with just
> one controller.
> 
> The card is advertised with
> 
>    The Adaptec SCSI Card 29320-R is a half-size, 64-bit 133 MHz PCI-X,
>    single-channel Ultra320 SCSI card with integrated HostRAID. The
>    29320-R includes a legacy SCSI connector and is a cost effective
>    hardware based RAID, a better alternative to software based RAID in
>    the market today. It provides worry-free data protection at the
>    fastest SCSI speeds available up to 320 MBps ideal for mainline
>    storage, streaming video and audio, and other bandwidth-intensive
>    applications. The card has a 68-pin HD external connector and a
>    68-pin HD internal connector for Ultra320 SCSI (LVD) hard disks
>    drives and a 68-pin/50-pin legacy SCSI connector. The 29320-R offers
>    an unparalleled degree of investment protection and upgradability to
>    Adaptec's entire SCSI RAID family of products.
> 
> It appears to have an "AIC-7901X" SCSI chip; would this card be
> supported by the ahd driver? The man page just mentions AIC-7901 without "X".

Well, calling it a "hardware based RAID" controller is stretching it a
little bit.

The HostRAID controllers are standard SCSI controllers with a special BIOS
that understands on-disk RAID metadata.

That special BIOS allows you to boot off the array.  Once the OS takes over
from the BIOS, though, it has to have a RAID stack that understands the
particular RAID metadata in use.

So you would need to modify vinum or ccd to understand Adaptec HostRAID
metadata, or you'd need to write your own RAID stack that would do it.

The format is available, for anyone who wants to do it.  The following are
pointers to Linux HostRAID implementations, which include the metadata
format:

http://people.freebsd.org/~ken/linux/md.html

http://people.freebsd.org/~gibbs/linux/SRC/emd-0.8.0-tar.gz

The first one is an older version, the second one is a newer more up to
date version.

Ken
-- 
Kenneth Merry
ken at kdm.org