ioscan and scsi - what does it mean?

[Rodney Hills]

I recently purchased an rp2470. The specs listed 2 internal Ultra Wide SCSI and 2 external SCSI's, one Ultra SCSI and one Ultra2 SCSI.

The ioscan of the system is as follows (The last 2 SCSI controllers I purchased seperatelly).

ext_bus 0 0/0/1/0 c720 SCSI C896 Ultra Wide LVD
ext_bus 1 0/0/1/1 c720 SCSI C896 Ultra Wide Single-Ended
ext_bus 2 0/0/2/0 c720 SCSI C87x Fast Wide Single-Ended
ext_bus 3 0/0/2/1 c720 SCSI C87x Ultra Wide Single-Ended
ext_bus 6 0/4/0/0 c8xx SCSI C1010 Ultra Wide Single-Ended A6828-60101
ext_bus 4 0/6/0/0 c720 SCSI C87x Fast Wide Differential

I just talked to HW support to get some clarification and was told the following-
The Ultra Wide LVD is an Ultra2 Wide LVD
The Ultra Wide SE is an Ultra Wide LVD (2 internal)
The Fast Wide SE is an Ultra Narrow SE
The Ultra Wide SE A6828 is an Ultra160

My understanding of SCSI definitions are-
Fast is 10 MHz, Ultra is 20 Mhz, Ultra2 is 40 Mhz, and Ultra160 is 80Mhz.
Narrow is 8 bit and wide is 16 bit (thus doubling throughput).

Am I misinterpreting SCSI from ioscan or are the descriptions just wrong?

-- Rod Hills

[Dietmar Konermann]

Rod,

you are right with your assumptions about the SCSI speed definitions and their naming. But you need to be careful how to interpret the ioscan output.

Essentially ioscan reports the configured limit for the interface. There may be a higher speed supported, but the setting in BCH (boot control handler) may restrict the maximum speed.

There are the prominent chip types used in today's interfaces:

C87x in ioscan:
LSI53c875 Wide Ultra SCSI chip
LSI53c876 Dual port Wide Ultra SCSI chip

C895 in ioscan:
LSI53c895 Wide ULTRA2 SCSI chip

C896 in ioscan:
LSI53c896 Dual port Wide ULTRA2 SCSI chip

C1010 in ioscan:
LSI53c1010 Dual port Wide UTLTRA3 SCSI chip
(aka Ultra160, used for single and dual port)

In ioscan you see the speeds "Fast, Ultra, Ultra2 or Ultra160", depending on your settings in BCH.

From your ioscan extract only the C87x on 0/0/2/1 seems to run in NOLIMIT mode.


Best regards...
Dietmar.

[Rodney Hills]

Dietmar,

Thanks for the info. I've been trying to get up to speed on SCSI speeds/types.

To paraphrase, are you saying since all my descriptions are Fast or Ultra, I have no Ultra2?

I know the controller on 0/4/0/0 is an Ultra160 (I got the disk drives), but it does not mention Ultra160.

Also, you said 0/0/2/1 is the only "UNLIMITED". Does this mean I can't boot from that disk? I planned on mirroring the 2 internal disks for vg00.

If their is a document that helps explain this I would gladly research on my own.

Thanks,

-- Rod Hills

[Jeff Schussele]

Hi Rod,

The final point - bit-width - strictly deals with addressability. 8-bit SCSI can have - at most - 8 devices. Whereas 16 bit can address 16 devices. 8-bit can have SCSI IDs 0 -to-> 7 and 16 bit 0 -to-> 15.
Doesn;t have anything to do with throughput - just device addressability.

HTH,
Jeff

[Rodney Hills]

Jeff,

The documents I have seen show-
Fast-SCSI is 10 megabyte/sec
Wide Fast-SCSI is 20 megabytes/sec

Ultra-SCSI is 20 megabyte/sec
Wide Ultra-SCSI is 40 megabyte/sec

So Wide does increase throughtput, 16 bits of data versus 8 bits.

I know that 16 bit also allows you more addresses for devices.
LVD is also a factor in number of devices.

Single-Ended versus Differential can determine the length of cable you can use.

It is difficult to keep the terminology straight, especially when vendors use it differently.

-- Rod Hills

[Jeff Schussele]

Hi (again) Rod,

I agree that the terminology can be easily confusing, but I think we're both correct here.
See the following from the Adaptec glossary:

\Quote
WIDE SCSI
Provides for performance and compatibility enhancements to SCSI-1 by adding a 16- or 32- bit data path. Combined with Fast SCSI, this can result of SCSI bus data transfer rates of 20 MBytes/sec (with a 16-bit bus) or 40 MBytes/sec (with a 32-bit bus). SCSI may now transfer data at bus widths of 16 and 32 bits. Commands, status, messages and arbitration are still 8 bits
\EndQuote

So it's the bus-width that gives the performance increase & that's where the confusion begins.

And this from scsimasters.com

\Quote
Ultra
A term used to describe a SCSI defined synchronous transmission rate of between 10 MHz and 20 MHz.

Ultra SCSI
A term used to describe an 8-bit wide bus operating Ultra (between 10 MHz and 20 MHz). The maximum data rate of an Ultra SCSI device or bus is 20 Mbytes/sec. Sometimes referred to as Fast-20.

Ultra2
A term used to describe a SCSI defined synchronous transmission rate of between 20 MHz and 40 MHz.

Ultra2 SCSI
A term used to describe a 8-bit wide bus operating Ultra (between 20 MHz and 40 MHz). The maximum data rate of a Ultra SCSI device or bus is 40 Mbytes/sec.

Wide
A term used to describe a SCSI bus that is 16-bits in width.

Wide Ultra SCSI
A term used to describe a 16-bit wide bus operating Ultra (between 10 MHz and 20 MHz). The maximum data rate of a Ultra SCSI device or bus is 40 Mbytes/sec.

Wide Ultra2 SCSI
A term used to describe a 16-bit wide bus operating Ultra (between 20 MHz and 40 MHz). The maximum data rate of a Ultra SCSI device or bus is 80 Mbytes/sec.
\EndQuote

Here you'll see where the term Ultra/Ultra2 more closely defines the speed increase. It's this terminology interchange that confuses me as well as many others I'm sure.

But you're correct i.e. the way HP uses the terminology, wide is essentially a data bus doubling that essentially doubles performance....and adds the address doubling at the same time. What's unclear to me is if we now have 32-bit busses, why can't we get 32 devices on the bus now?!?!?

Clear isn't it? ;~))

Cheers,
Jeff

[Rodney Hills]

Jeff,

Your definitions are pretty much what I found. I ready once that 32-bit was defined once and a standard set, but for some reason did not become popular.

The definitions you give (which is the way I understand the terminology) isn't lining up with what ioscan says.

::-)

(seeing double because my head is spinning)

-- Rod Hills

[Dietmar Konermann · Accepted solution]

Rod,

just to summarize again, the terms Fast/Ultra/Ultra2/Ultra160 only describe the maximum bus clock (10/20/40/80MHz). Together with the bit-width (Narrow/Wide, 8/16bits) the throughput is calculated, up to 160MB/s.

>To paraphrase, are you saying since all my descriptions are Fast or Ultra, I have no Ultra2?

An interface operating at Ultra2 speed would definitely show up as Ultra2 in ioscan.

Here's a short demonstration on one of our L-Classes:

The ioscan for 0/0/1/1 looks quite as your's:

ext_bus 1 0/0/1/1 c720 CLAIMED INTERFACE SCSI C896 Ultra Wide Single-Ended


This is what BCH says:

Main Menu: Enter command or menu > ser

---- Service Menu ------------------------------------------------------------

Command Description
------- -----------
CLEARPIM Clear (zero) the contents of PIM
SCSI [option] [] [] Display or set SCSI controller values
MemRead

[] Read memory and I/O locations
PDT [CLEAR] Display or clear the PDT
PIM [] [HPMC|LPMC|TOC] Display PIM information
ProductNum [] Display or set Product Number
ScRoll [ON|OFF] Display or change scrolling ability
SELftests [ON|OFF] Enable/disable self test execution

BOot [PRI|ALT|] Boot from specified path
DIsplay Redisplay the current menu
HElp [] Display help for specified command
RESET Restart the system
MAin Return to Main Menu
----
Service Menu: Enter command > scsi

Path (dec) Initiator ID SCSI Rate Auto Term
------------ -------------- ---------- ---------------

0/0/1/1 7 Ultra Unknown
...

OK, lets set it to "nolimit".

Service Menu: Enter command > scsi rate 0/0/1/1 nolimit

Path (dec) Initiator ID SCSI Rate Auto Term
------------ -------------- ---------- ---------------
0/0/1/1 7 No Limit Unknown

And after bootup ioscan shows:

ext_bus 1 0/0/1/1 c720 CLAIMED INTERFACE SCSI C896 Ultra2 Wide Single-Ended

q.e.d.

Best regards...
Dietmar.

[Rodney Hills]

Dietmar,

Thank-you. Now some of it is starting to click.

So even though a controller is capabable of Ultra2 speeds, it can be slowed down through configuration. And this is what ioscan will report.

I fetched the documentation from LSI on those chips and that helped explain on their capability.

I played around setting "NOLIMIT" and now I get the following from ioscan-
ext_bus 0 0/0/1/0 c720 SCSI C896 Ultra2 Wide LVD
ext_bus 1 0/0/1/1 c720 SCSI C896 Ultra Wide Single-Ended
ext_bus 2 0/0/2/0 c720 SCSI C87x Ultra Wide Single-Ended
ext_bus 3 0/0/2/1 c720 SCSI C87x Ultra Wide Single-Ended
ext_bus 6 0/4/0/0 c8xx SCSI C1010 Ultra Wide Single-Ended A6828-60101
ext_bus 4 0/6/0/0 c720 SCSI C87x Fast Wide Differential

The C896 has 2 Ultra2 Wide ports,
- 1 is external (I had DDS-4 tape drives, and they still worked after change)
- 1 is the internal disk drive and is set at Ultra
The C87x has 2 Ultra Wide ports
- 1 is external (previous defined as Fast, but now Ultra when I set NOLIMIT)
- 1 is the other internal disk drive
The C1010 has 2 Ultra160 ports (as defined by LSI)
- Only 1 port is available as an external port
- ioscan still reports it as only "Ultra", but I guess I should ignore that

It still bothers me a little that they say Single-Ended, especially on the c1010.

I guess if it works then I should be happy.

I want to thank all for your input. I found it very enlightening.

-- Rod Hills

[auser]

Hi

does anyone know the exact specs of C896 scsi card ?

wat is the max throughtput? is it 160 MB/s?