Dumb SCSI question....ready for the pain!

[SaigonK]

Ok so here we go....


I recently inherited an Adaptec 2940uw PCI card with what appears to be the following:
68pin internal/50pin internal/50 pin external (sound right?)
I also got an Adaptec 2940 card with what appears to be a single 50pin connector.


I have some 68pin and 50pin cables that came with them, but I am wondering a few things and was looking for some insight from the scsi users here at Anandtech


Questions are:


A. What drive would go best with the 2940uw? Size? Make?
B. What drive would go best with the 2940? Size? Make?
C. Do i need any other parts to complete the setup? Terminators ( i think) etc etc?


What i want to do is pop the 2940uw (since it is the better card) into my Asus CUSL2 and then install a SCSI drive with it.

Any suggestions?

Thx!

 

[Magicthyse]

First of all, I don't think it's worth hooking up the adaptor to your CUSL2 if your needs are for hard disk only.

Here's why - the AHA-2940UW (Ultra Wide) is a UW-SCSI controller, whch equates to 40MB/sec SCSI bus throughput. The 2940 is a Fast SCSI card, which equates to 10MB/Sec SCSI throughput. Since I think the CUSL2 has at least ATA66 onboard, unless your plans are to run more than 3 hard disks at once, it's a retrograde step.

I don't therefore think there's much point in installing the card, unless you have other SCSI devices to connect - use IDE for the HDD.

 

[Magicthyse]

Perhaps other people will read this as well, I see a lot of SCSI questions here...
Just a quick explanation of SCSI I thought might be helpful to add:

USCSI and UWSCSI I've already explained:
USCSI typically has support for 7 devices in total @ 10MB/Sec for the single SCSI chain. Adaptec card - AHA-2940
UWSCSI, typically 15 devices @ 40MB/Sec for the single SCSI chain. Adaptec card - AHA-2940UW

The above are ideal for CD-ROMs, DVD-ROMs, scanners, Zip disks and so forth.

U2WSCSI (Ultra 2 SCSI), 15 device support in total @ 80MB/Sec for the chain. Adaptec card - AHA-2940U2W.
U3WSCSI (Ultra 3 SCSI or Ultra160), 15 device support per SCSI chain @ 160MB/Sec for the chain. Adaptec card - 29140

These are the controllers to use for hard disks at the moment. Plugging slower-speed devices like zip disks into a U2W/U3W port will typically drag the entire SCSI chain speed down to USCSI.

SCSI v IDE?
SCSI is only really useful if you have a need to attach multiple hard disks on a single machine (more than 3) - especially in drive striping and fault tolerant configurations, or if you have an absolute need for blazing speed (Ultra 160 SCSI drives with 15,000rpm speeds are becoming available). With multiple drives, SCSI also becomes much more efficient than using multiple IDE cards - whereas SCSI is actually slower in a single-drive situation than IDE of the same speed (i.e. a U2WSCSI hard disk will perform only marginally faster than an ATA66 IDE drive / ATA100 controller combo if in a single hard disk scenario).

 

[SaigonK]

yes, but wont it be continous output?
I know that IDE "brags" about ata-66, 100 and 133 but they rarely come anywhere near that mark.
I am sure someone once posted that testing showed they really on hit 30-40mb max throughput (continously)

Wrong or right?



EDIT:

One reason I am interested is that i have a friend with an Abit BF6 and IDE drives.
he has a DV500+ video editing solution and he is looking for more speed when it comes to rendering etc etc......would the 2940uw at 40/mb be of much use to him?
I am assuming it is a continous 40/mb which must be MUCH better than his Dma-33 on his BF6..
??? ?

 

[Magicthyse]

Actually, ATA33 isn't that much slower than UWSCSI in single and possibly two-drive configurations.

You have to also bear in mind that the drive itself (in both SCSI and IDE) does not supply the full chain speed - i.e. there is no way a single drive, even a current state of the art one, is for example going to stress a U160 chain on its own. The U160 speed is for the whole chain of 15 max devices.

The IDE tests were I am sure done with one or two drives. The key fact is that in near-equivalent version of SCSI, you can expect much the same throughput from the same number of drives. If you for example get 40MB/Sec out of a single 7200rpm IDE drive, you will probably get similar - maybe even less - out of a single SCSI drive on a U2SCSI chain.

Either way, unless you're going to run 4 drives or more, UWSCSI is not a significant improvement over even ATA33, and certainly not ATA66.

 

[Marine]

On the other hand, I use 2940 controllers, currently 2940 U2W Pro, because I have three SCSI HDDs, a SCSI DVD, a SCSI CD-ROM, a SCSI CD-RW, a SCSI scanner...and so on. I'd soon be out of both IDE connections as well as CPU cycles if I tried to drive all this off the IDE bus and ask the processor to display 3D graphics as well. The SCSI controller manages the data flow so the processor doesn't have to and even in a mid-grade machine frees up those cpu cycles for applications rather than using them up in moving data around. The 2940s are cool because you can use an Adaptec cable to connect external devices on the internal bus. Wouldn't build a computer without them...although they are a bit more expensive than IDE parts. Hmmm...wonder why that is?

 

[SaigonK]

So for the video editing solution it would be better to go with 2 SCSI drives instead of 1? (ide or scsi)
This way the CPU is free to do what it wants and the SCSI card/drives are doing all the work when exporting the final product?

 

[Magicthyse]

Perhaps I didn't make it clear.

Both the SCSI adaptors that you have are WAY slower than ATA66 even. Therefore, it doesn't make sense to use the 2940UW with current SCSI hard disk drives.

Marine has a 2940U2W - I've got one as well, although not in a PC at the moment, which offers double the SCSI chain speed compared to a 2940UW, as well as simultaneous support for UW devices on a separate chain.

Unless you can get your hands on a 2940U2W or better (29160 for example) and run 3 drives or more, it doesn't really make make sense not to use the built-in ATA66/100 on the CUSL2. IDE is not that bad processor-wise in two drive configurations.

 

[Colt45]

SCSI rates are sustained, use less cpu power, and overall better IMO
im pretty sure a 2940 can do 20mb/s (Ultra SCSI or Fast SCSI, maybe SCSI-2, i forget)
{because the 50pin on my 7880 can do 20mb/s}
10mb/s is just plain 'ol scsi-1 i believe.
2940UW is UltraWide SCSI and is 40mb/s