[Phoenix1997]

I have a small SCSI drive enclosure:
http://mercury.made2...~eiiisol/s3.jpg
It accepts three 80 pin drives and has two 68 pin connectors on the back.
I'm running this on an Adaptec 29160 card (U160).

If I have one drive in there (Fujitsu MAM series, U160, 36GB), it works just fine. My burst read speed is ~83MB/sec, which is close to the 88MB/sec which Fujitsu has rated this drive for. If I add a second drive (Fujitsu MAS series, U320, 36GB), the burst read speed for both drives drops to about 62MB/sec. The MAM is limited to about 58MB/sec off the interface, but the MAS is capable of faster speeds!

The random access times are still great, 6.0 and 5.6ms for the MAM and MAS, respectively (HDTach).

I'm guessing the domain validation thingy of U160 is kicking in. What can I try to do to fix this? I've tried two different cables, both terminated, but they're only connected to one of the connectors on the back of the enclosure. It seems to help a little if I connect another connector on the cable to the second connector on the box; with 3 drives in there, Windows won't start if the drives are synced at 160 with only one connector, but will with two. The MAM is on top, (device ID 0) and the MAS is on the bottom (device ID 2). If there were a drive in the middle it would be device ID 1 (I have an older Compaq 15K U160 I can use in there).
Even if the MAS is on its own inside the enclosure, and on its own cable, it's still stuck at 62MB/sec. Is poor signal quality to blame or the fact that the drive's expecting a U320 environment?

[jamesbzx8]

Hello,

I am presently toying with various Enterprise class caching RAID controllers, mostly U160 ones and a couple of U320 ones.
I am also using 6 Fujitsus' MASxxxx and 3 MAUxxx. I also get access times like you are getting with HDTach, around 5.4-5.6mS.

I would definitely change your cable wich is one of your source of frustration. I have toyed with an old semi-rigid Ultra cable, its' termination was choking my drives. I then employed proper semi-rigid BRAIDED , terminated U320 cables.

These BRAIDED cables are from FoxConn and have connectors for 4 devices. Igot them from STSI.com from eBay. They are working without a hitch. They are reasonably priced around 15-18 dollars $US.

I have no idea if your Hybrid SCSI backplane case is of sound design.

You might also want to look at your motherboards' BIOS setting that could bottleneck your setup. This setting is called PCI Latency Timer: older motherboards used to have this set at 32. You should try to have it at 64: newer mobos have this value now set by default in the BIOS.
Here is a linky to the Great Adrian Rojaks' BIOS setting guide:

http://www.adriansro...S_Guide_02h.htm

Another possibly overwhelmed device might be the 29160, its processor was designed long time ago and having no cache, might be further limiting STR if you RAID0 the drives you have. This HBA ( Host Bus Adapter) came out when SCSI drives weren't speeding demons like the nice 15K drives you have.

I hope that my suggestions help you in your quest and also that you don't feel all alone ;-)

Enjoy!
JB

[discjet]

My guess based on zero experience about scsi enclosures is that you need to have a non-terminated cable that has one end connected to the 29160 and the other end to your scsi enclosure, and then put a terminator to the other connector of the enclosure.

[jamesbzx8]

Very good observation Discjet!

My assumption is that it is a hybrid backplane and probably expects to receive a stand-alone terminator on the back 68 pin connectors.

If the initial poster would reveal the brand of this backplane/enclosure, it would cut down on assumptions ;-)

Thanks for participating :-)

[Phoenix1997]

The fact that I'm running this on an old BF6 might have tipped me up to the fact that it's an old board.
I raised my PCI latency timer from 8x4 to 8x31, and that got me an extra 20MB/sec:

If I raise the PCI clock speed to 37.5 MHz the burst transfer rate gets to about 86MB/sec.
Don't worry, this drive will end up on a newer board. Thanks!

[Phoenix1997]

Interestingly enough, there was something else on the PCI bus which I hadn't thought of - my USB to 802.11g adapter. Removing that upped the transfer rate to 106MB/sec.
It's frustrating to have drives so fast that everything else on the PCI bus slows them down. Or is it?