SCSI RAID Array troubleshooting, capped at 50mpbs

[Cactus]

Hey everyone, been posting this around a few forums now, but nobody seems to know what my issue here could be.

I'm running x2 "ICYDOCK (sometimes known as CREMAX) MB-016CKDF-B" SCSI enclosured, inside each is three SCSI Seagate 15k RPM U160 18GB (cheetahs)

These each go to seperate channels on a Dell Perc3/DC, via two U320 terminated cables.

I've tried running on several SCSI arrays, even to the point of using the drives as seperate singular drives, no dice.

Everything is U160 compatible.

No matter what i do i cannot get it to run at proper speeds, its just capped at around 50mb

Heres some screencaps of its performance compared to my ye olde SATA drive currently in there.

SiSandra http://i34.photobucket.com/albums/d127/cactus57/01SiSandra-RedSCSIarray-Orangesingl.jpg
SiSandra http://i34.photobucket.com/albums/d127/cactus57/02SiSandra-RedSCSIarray-Orangesingl.jpg

Atto SCSI http://i34.photobucket.com/albums/d127/cactus57/03ATTOSATA.jpg
Atto SATA http://i34.photobucket.com/albums/d127/cactus57/04ATTOSCSI.jpg

I spoke to the manufacturer of ICEYDOCK stuff and they told me that it *might* have to do with there not being a terminator on the output of the docks. Although my SCSI cables are terminated, this may not be enough.

So now, I'm oddly capped at 50mpbs and i can't figure out why.

Everything i have is 160 compatible and nothing is close to a 50mbps limit, also the fact that cross-channel striping give me NO GAINS at all, makes it even weirder.

Anyone have any idea why its limiting me to 50mbps?

Any help greatly appriciated :)

[tiro_uspsss]

might need to go to 2CPU forum - they have a few more fellows dealing with SCSI RAID arrays over there :up:

[stevecs]

Have you tried running the drives directly attached to the card (not using the icydock?) I've seen similar items in the past with hot-swap and other attachments where the separation chipsets used in the housings were not able to handle more (some were just capped, others would produce parity errors in the chain which would force retransmits on the bus).

If possible, check with a single drive attached to the controller directly. This would not require any termination (HBA is terminated and with one drive there is not enough on the bus to cause any problems. Then move to two drives w/ a terminator and try again.

[Cactus]

Yeah, i tried 2CPU, no luck there either.

I'd try attaching them directly but i think the amount of pins needs converting (U320 > U160?) and i have no adaptors.

I'll try and sort it out to connect one directly, but i don't think i'll be able to without throwing more money at it.

I contacted IceyDocks higher end user support (blokes who actually know what SCSI is) and they couldn't figure it out either, their only idea was to put terminators on the Docks output.

I think it's just going to be easier to sell it and buy a decent SATA drive tbh. Certainly be a lot quieter.

Cheers anyway fellas, if i can sort out a single drive on it through i'll post back with results. Thanks for giving it a shot anyway :)

[stevecs]

U320/U160/U80/Fast-wide 40 et al are all the same. It's just a clocking difference. The connector is probably a 68pin on the back of the drive and your internal on the card is 68 pin as well if I remember right on those perc cards (if it's 50 that's one problem). Scsi is completely downward compatible down to SCSI-1 spec (5MB/s)

Your drive should have a 68pin connector on the back of it (it could also be 80pin SCA but you would probably know that if it was as you'd have to buy the right dock station).

Without knowing exactly what drive you have, the 50MB/sec figure itself is not bad (that's about right for many of the older SCSI drives for a single drive). What is the make/model # of the drive?

[jackies]

So what is your mobo?
Because you will be getting 50mbs transfers if Dell Perc3/DC is plugged into regular pci, as opposed to pci-x..
Or maybe your pci-x settings are not up to par..
I been running similar setups for a while, and let me tell you this: 50mbs on 15k scsi is alot snappier than slow 7200 (or even 10k) sata drives. Most important number in hdd performance is not sustained transfer but average seek time, especially for windows/program files.
I'm using 15k scsi for windoz and sata for big files.

[Cactus]

I am just using a regular PCI slot, but i was told my limit on that was 150mbps?

My disks are these: http://www.impediment.com/seagate/s2000/spec_318404lc.shtml

The drives are 80 pin, which means they won't plug right into my cables i guess. So that kinda rules out testing them outside of the dock.

The 50mbps limit is odd because it means i have no gains when striping cross channel.

And to be totally honest, i didn't notice any gaming improvment playing games (which use the HDD alot, such as Oblivion), and thats really the only thing i wanted a performance boost on. And seeing as my current SATA drive is outperforming my SCSI array, well, theres little reason to keep it.

If the PCI sot was the limit, it would make sense and explain why I'm getting no gains regardless of the setup.

[stevecs]

The PCI bus is limited to a max of 132MB/sec real-world you will be hard pressed to get more than 100 though through it. Those drives you have are SCA drives (LC) which use the 80pin power/data combined connector.

Also those are older drives (actually have a stack of them here on my desk that I use for some modern art. ;) ) Those drives you're not going to get more than that 50MB/sec each (actually that's quite good). Generally you put more of them on a bus to get better speeds. For an u320 bus you could probably get 12 or so comfortable on each channel before bus contention really kicks up.

Striping only helps when you have a request size that will span across multiple stripes OR if you have a larger request queue (more than 1). With a home system that is not that easy. You will probably not see much improvement with just a single disk with games et al. Games hit the drives when loading up each section which is a streaming request. That is capped at your drive speed (usually related to bit density). Where the faster RPMs come in is helping with latency which is a multi-I/O workload this is not something you generally have on small home systems.

The limit you are hitting right now is the single drive, after 2-3 of those drives you will hit the bus limit of PCI (assuming you're streaming and have requests that will span all drives).

[jackies]

Well the PCI slot is defenitely the limit because I have the similar setup and same 50 mb limit. Yet I tried installing windows on sata drive, it feels slower.
So I just bought a mobo with pci-x and will experiment and see how much faster that will be...
As for games, videocard is the stuff..
:D

[stevecs]

Umm, per the spec sheet that drive has a max internal transfer rate between 33MiB/s to 50MiB/sec (inner/outer track).

http://www.seagate.com/support/disc/manuals/scsi/75789506g.pdf

A faster bus than PCI for a single drive is kind of moot. It's only when you have multiple drive and only when you do streaming reads will that start to be a cap. But these types of drives (15K et al) are not really designed for streaming but for random I/O. If you're looking for just streaming you'll get _MUCH_ better performance looking at low RPM but very high density drives.