Date: Thu, 30 Sep 1999 12:36:21 -0400 From: Michael Meissner <meissner@cygnus.com> To: Gregory Hosler <gregory.hosler@eno.ericsson.se> Cc: Michael Meissner <meissner@cygnus.com>, aic7xxx@FreeBSD.ORG, noe@monet.prism.uvsq.fr Subject: Re: fast drives. Message-ID: <19990930123621.A2140@tiktok.cygnus.com> In-Reply-To: <XFMail.990930152527.gregory.hosler@eno.ericsson.se>; from Gregory Hosler on Thu, Sep 30, 1999 at 03:25:27PM %2B0800 References: <19990929093341.C4929@elmo.cygnus.com> <XFMail.990930152527.gregory.hosler@eno.ericsson.se>
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On Thu, Sep 30, 1999 at 03:25:27PM +0800, Gregory Hosler wrote: > The interface is an motherboard AIC-7896. I don't recall if I mentioned that this is the controller I have. > The Seagate is, to the best of my knowledge, fast/wide only. Question: > how do I tell if it is "SE" ? (the adaptec reports it as "SE". Ignorant > question time. What's "SE" ?). I know that the Seagate is not LVD. If it is fast/wide only, it is definately SE (single ended). > The IBM is jumperable LVD or SE. To be honest, I am not sure the present > setting. I have tried both in an attempt to get it to register at BIOS > probe setting at 80.0 MB/s, but to no avail. I have seen other posters > using this drive, so there must be something I am likely doing wrong. > > more ignorant questions: > > 1) As I am learning, I am now (only now) guessing that it might not be a > good idea to combine LVD and SE on the same scsi bus. > is this true ? That's what people say. On my system, the guy who built it, put the two LVD drives on one scsi channel and jumpered it as LVD, and the cdrom/tape on the second scsi channel jumpered as SE (I have since added another scsi controller and put the slow devices on it, and connected the 3 older disks via an internal/external connector. > 2) are there any special cabling / termination issues with respect to LVD > that are different from SE scsi ? LVD cables are different from SE cables (the LVD cables I've seen are multi-colored and twisted, while the SE cables are flat gray ribbon cables). As others have mentioned the terminators are completely different two. I would imagine that LVD cables are more expensive than SE cables. > 3) How do I get my AIC to recognoze the IBM at 80 Mbs transfer rates ? > (do I need to move the Seagate to a different scsi bus ?) Until you get to 3 high end disks, you probably won't notice any speed difference between 80 Mbs and 40 Mbs. This is because high end disks can only deliver data in the 10-20 Mbs range -- what the scsi controller speed of 80 Mbs measures is the total bandwidth spread over all devices. So one option is to just jumper the IBM disk as SE and use SE cables and an active terminator. Obviously you can separate the two disks into the different scsi buses too. > Cableing: > > The scsi's are in an external box. The cabling in the box is blue and flat > but not the typical "flat ribbon" cable. supposedly it is specifically for > the faster disks, but I'm not sure what it should really be, and I don't > know (for sure) what it really is, except that it is not the standard > 68 wire wide flat ribbon cable. The external box is terminated with an > "active terminator" and teh other outlet of the box is connected to the > pc box by a heavy duty 100 ohm 68 pin cable. The pc box to motherboard is a > 68 pin "twisted pair" cable. (lots of loose wires, nothing at all like a > ribbon cable). That twisted pair cable is probably an LVD cable. > The setup works much of the time, especially under no load (the > non-interesting and trivial case, unfortunately). Under load, it fails > w/ vaarious messages, usually starting w/ complaints such as the > following: > > No active SCB for reconnecting target > > or some time out error. > > My 1st step was to disable tagged queueing (at the driver compile level). > This significantly reduced the occurance of the problems, but not > eliminated. The next step was to reduce the transfer speed in the > Adaptec BIOS. I went from 40.0 to 32.0 - I am still getting time out > errors (though less frequently). > > It occurs to me that by disabling tagged queueing, and reducing thruput > to 20mb, or less, I have totally defeated the purpose of buying a 80.0 > mb drive (which at best I can only seem to get seen as 40.0 mb). See above for 80 Mb vs. 40 Mb. However by turning off tagging, you are reducing the speed of the disk. > I am really discouraged, and at the point of seriously contemplating > switching adapter cards, the only thing is that the AIC is on the mother > board, and is one of the reasons I bought this particular mb. > > -Greg > > > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe aic7xxx" in the body of the message -- Michael Meissner, Cygnus Solutions PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886 email: meissner@cygnus.com phone: 978-486-9304 fax: 978-692-4482 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe aic7xxx" in the body of the message
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