Date: Tue, 29 Jan 2002 09:26:36 -0500 From: Jason Andresen <jandrese@mitre.org> To: ptiJo <ptiJo@noos.fr> Cc: freebsd-questions@freebsd.org Subject: Re: divers SCSI questions... Message-ID: <3C56B11C.2C8CB6A7@mitre.org> References: <20020128230531.20f8d55b.ptiJo@noos.fr>
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ptiJo wrote:
>
> Hi,
>
> as I never played with SCSI and get an old PCI Card, I would like to be enlightened a bit :)
> so, I got the "Adaptec AHA-2940UW" which specs are:
Ok, this is a slightly older but perfectly good card.
> Computer Bus:
> PCI Local Bus
> Interface Protocol:
> Bus master DMA
> Host Bus Burst Data Rate:
> 133 MByte/sec
> Peripheral Bus:
> 8-bit and 16-bit Wide UltraSCSI
> SCSI Synchronous Data Rate:
> 40 MByte/sec
> SCSI Asynchronous Data Rate:
> 3.3 MByte/sec
> Device Protocol:
> SCSI-1, SCSI-2, SCSI-3, Wide UltraSCSI
> Device Support:
> Up to 15 devices under DOS 5.0 and above
>
> Here are the questions :)
> -1- does the data rates specify that, in general, the transfer rate is 3.3 MBytes/sec ?
In general you will get 40MByte/sec with your drives (well, peak at
least), at least with the
drives listed below. SCSI has several different speeds, with different
names. Your card supports
40 MB/S (SCSI-II Ultra Wide IIRC). The hard drives below are capable of
160MB/S (SCSI-III LVD). Since the limiting factor is your card you will
get 40MBs throughput.
> -2- 15 devices under DOS... would it be more under FreeBSD ? is there also a limitation on total size that I would get (15*36Go or 15*9Go, for eg) ?
15 devices is a SCSI limitation, and that's only for the newer SCSI's
(old SCSI was limited to 7).
Technically it's actually 16 devices, but the SCSI card itself counts as
a device.
> I would like to buy disks now :)
> IBM 36 Go 10000 RPM SCSI
> IBM 18 Go 10000 RPM SCSI
> IBM 9 Go 10000 RPM SCSI
>
> -3- do I have to take special care ? I mean, the supported device protocol are SCSI-{1,2,3} and Wide - do all disks (like those recent above) supports @least one of them ? Or do I have to check the disks specs to see which protocol they support ?
SCSI support is layered. Since the drives above support LVD (I think,
double check that), then they should support Ultra Wide.
As for special care: Make sure each drive is set to a different device
number (Setting them as
1, 2, and 3 might be a good idea). This will be done by setting jumpers
on the back of the
drive. Also, make sure you get a good cable, crappy cables are the bane
of SCSI. Finally, the SCSI bus needs to be terminated, on the internal
side this is easy to do--just plug a drive into
the last slot on the cable.
--
\ |_ _|__ __|_ \ __| Jason Andresen jandrese@mitre.org
|\/ | | | / _| Network and Distributed Systems Engineer
_| _|___| _| _|_\___| Office: 703-883-7755
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