SCSI wiring  - Page 1
Forum section: electronics / general

author: legacy
author_rank: Super Contributor
timestamp: May 19, 2016, 02:11:01 pm
content: hi thereI have a very strange problem here, my boss wants to use { LTO2 tape drive, DDS4 tape drive, CDRW, CF-to-SCSI} units, to be installed inside an enclosure, which offers two SCSI channels, both wired to a pair of 68p connectorsLTO2, 68p female, assigned to channel1DDS4, 68p female, assigned to channel1CDRW, 50p male, assigned to channel2CFRW, 50 male, assigned to channel2the enclosure comes with a back-plane which offers two pair of 68p connectors per channelideas ? suggestions ?thank you in advance

author: legacy
author_rank: Super Contributor
timestamp: May 20, 2016, 07:07:49 am
content: as far as I have learned, normally there are 2 connectors on the outside of an external enclosure. One goes to the host, the other is terminated or goes to the next enclosure. Inside, between them, a flatcable with a couple of male connectors you plug into the devices, therefore the SCSI toplogy *must* be a single chain with a terminator at the end, and you cannot create a branch, a 'T' or something, because they violate the standards and when it happens bad things might happenso, the new topology should look this wayCode:external | internalhost_cable ---- HD68/female ---+bracket+----68p/female-----1+ 68p/male||cable 68p|2+-- 68p/female unit1|3+-- 68p/female unit2|4+ 68p/male+----68p/female-----bracketterm ---- HD68/female --+Code:internal cable:68p/male ---- 68p/male ---- 68p/male ---- 68p/male(1) (2) (3) (4)Code:-------------------------| |HD68/female --- bracket --- 68p/female| |-------------------------what do you think?do you know a shop, or a company, which realizes a customized SCSI cable ?

author: legacy
author_rank: Super Contributor
timestamp: May 21, 2016, 07:42:51 pm
content: do you know, guys, an online shop which sells SCSI accessories(cable, brackets, adapters, terminators, etc) ?I can see them on ebay, but ... it seems I can't buy one shot,which means too much money wasted in shipping costI am not sure about the keyword I used in the above scheme,and I am not sure it's correct, feel free to suggest(including better solutions and criticisms)

author: C
author_rank: Super Contributor
timestamp: May 21, 2016, 10:54:23 pm
content: Quote from: legacy on May 19, 2016, 02:11:01 pmNot enough information. You need to know what version of SCSI each device is using to do a good job.Better readhttps://en.wikipedia.org/wiki/Parallel_SCSIYou could easily have 8-bit bus or 16-bit bus with single ended or differential drivers.Depending on computer use, you could run into buss speed limits causing some operations to fail or be hard on the devices.If you think back in time, not getting information to a CDRW fast enough ruined the CD you are trying to create. For the tape drives this becomes a backup and get up to speed to read/write a block of data.One use case could be a copy from one tape drive to the other tape drive. If the buss is to slow, you would have to use the PC to buffer more data and this would still slow the copy. The cure would be two controllers and two separate buses.Just guessing 68 to 50 will be a shift from 16-bit buss to a 8-bit buss with the adapter adding termination to the unused 8-bits on the buss. If the adapter is built to plug in to a drive this termination may not exist where a cable to cable adapter would have the termination.Later generation 68-pin SCSI cables are also different.So step One, what SCSI standard is each device?

author: legacy
author_rank: Super Contributor
timestamp: May 22, 2016, 12:12:58 am
content: on the host side, the SCSI service comes with two UW SCSI controllers based on the QLogic 1040B chipset, one is used to support the three internal drivebays (SCA connectors), while the other can be used for external devices using the 68pin connector on the back of the machine, they are SE, and the maximum bandwidth using both channels is 80 Mbyte/sec, as each SCSI subsystem has a bandwidth of 40 Mbyte/secthis happens in the built-in SCSI, but I also have two PCI boards in the PCI-expansion bay2xQLogic 1040B chipset, ~ 40 Mbyte/sec, SE/LVDDual-port U160 QLOGIC QLA12160@66MHz 64bit PCI SCSI card (LVD over VHDCI connections), 160 Mbyte/secthe last one is attached to a RAID-SCSI, therefore I can only use the two UW channels offered by QLogic 1040Ba DDS-4 unit comes with a Native Burst Transfer Rate of 10Mbytes/sec, while an LTO2 unit comes with a Native Burst Transfer Rate of 40 Mbyte/swe haveLTO2 unit, SCSI-3, 16bit, LVD/SE, 40Mbyte/secDDS4 unit, SCSI-2, 16bit, LVD/SE, 10Mbyte/secDLT unit, SCSI-2, 16bit, LVD, 6Mbyte/secCDRW-8X unit, SCSI-2, 8bit, SE-only, 4Mbyte/secCFRW unit, SCSI-2, 8bit, SE-only, 6Mbyte/secedit:these units don't need to access the bus concurrently, just one of them per time

author: legacy
author_rank: Super Contributor
timestamp: May 22, 2016, 12:27:44 am
content: I also happen to have these kind of tape-unitsIBM Seagate TC4200-122, DDS4, LVD/SE, ULTRA2, 68-pinIBM Half-High LTO2 LTO2, SCSI/LVD, Ultra160, 68-pinULTRA160 (aka ULTRA3)? ummm interesting, it's also declared24 Mbyte/secuncompressed48 Mbyte/seccompressedwith a memory buffer of 64 Mbyte, able to read&write LTO Generation 1 mediaedit:LTO2 doesn't need to compress data, therefore it will go 24Mbyte/sec

author: legacy
author_rank: Super Contributor
timestamp: May 22, 2016, 12:31:28 am
content: "CFRW "stands for CompactFlash reader/writer, it's a p/ATA device converted to SCSI

author: DimitriP
author_rank: Super Contributor
timestamp: May 22, 2016, 02:27:59 am
content: Candy store:http://www.pc-pitstop.com/scsi_adapters/

author: C
author_rank: Super Contributor
timestamp: May 22, 2016, 02:35:07 am
content: Here are some quick linkshttp://ask.adaptec.com/app/answers/detail/a_id/9/related/1http://ask.adaptec.com/app/answers/detail/a_id/3333/related/1http://ask.adaptec.com/app/answers/detail/a_id/1971ULTRA160 To get to this speed the time delays on the wire had to be compensated for. A test of controller to each device was used.

author: bitseeker
author_rank: Super Contributor
timestamp: May 22, 2016, 05:55:21 am
content: @legacy,I'd keep all the 8-bit SE-only devices on one bus and the LVD ones on the other. Otherwise, the faster LVD will be forced down to SE. Also, that alleviates having to adapt between 8- and 16-bit bus sizes as well as device order and potential termination issues.Lastly, keep the Ultra devices on their own bus to allow them their maximum performance.

author: legacy
author_rank: Super Contributor
timestamp: May 22, 2016, 10:12:01 am
content: Quote from: bitseeker on May 22, 2016, 05:55:21 amalready plannedLVD-units go to channel1LTO2, 68p female, assigned to channel1DDS4, 68p female, assigned to channel1SE-units go to channel2CDRW, 50p male, assigned to channel2CFRW, 50p male, assigned to channel2

author: legacy
author_rank: Super Contributor
timestamp: May 22, 2016, 10:32:32 am
content: Quote from: bitseeker on May 22, 2016, 05:55:21 amphysically we have two channels and I can't add a third one, the LTO2 is declared "Ultra3", but (since we don't want compression in our tapes) it needs a bandwidth of 24Mbyte/sec, therefore I believe it can work along with the DDS4 (Ultra2) without troubles

author: legacy
author_rank: Super Contributor
timestamp: May 22, 2016, 10:39:06 am
content: Code:external | internalhost_cable ---- HD68/female ---+bracket+----68p/female-----1+ 68p/male||cable 68p|2+-- adapter(68p/female,50p/female) --- 50p/male unit1|3+-- adapter(68p/female,50p/female) --- 50p/male unit2|4+ 68p/male+----68p/female-----bracketterm ---- HD68/female --+physically the enclosure has two pair of 68p connectors, two channels, each channel has two connectors. About SE-8bit units, I was thinking about the above topology, using adapters (68p/male)->(50p/female)what do you think ?

author: legacy
author_rank: Super Contributor
timestamp: May 22, 2016, 12:35:13 pm
content: about the above scheme, I am consideringthisadapter, 68 to 50 pins, female to female

author: C
author_rank: Super Contributor
timestamp: May 22, 2016, 08:18:11 pm
content: Wire plan looks ok.Adapter?should be just 68 to 50 with no terminator connected directly to back of drive.Think this is what you have here could not find good details.Might OHM 68 side high byte pin to high byte pin = openSuggest that you chose drive ID's with slowest toward 0. I would pick a different drive ID for each device even with there being two buses.If you have need for compressed on fast tape drive all you should have to do is pull other tape drive loose and may need too run bus tunning step.Notes:No terminator on your listed devices.Terminator Power from controller or one device.when you get it working,. test test test.

author: bitseeker
author_rank: Super Contributor
timestamp: May 23, 2016, 01:33:07 am
content: Yep, you're on the right track. As C said, be sure to do plenty of testing. That's quite a smorgasbord you've got going.