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Got SCSI ?

W

woolmilk

Member

Yeah, I want it all, all HD performance thats available 😀 !
So I put my money on ebay and got me a mylex170 and 2
15K rpm HDs.
One Compaq 15K SCA and one Cheetah 36LP both 18GB,
though I first thought that Compaq beast is the older Cheetah.
Both are reported 80Mhz with 16Bit, thats U160, right ?
That should do the job, so i plugged them together and started benching. Both harddrives showed nearly the same throughput.
Well, for a single drive, the benchmarks are really good.
Atto shows 35MBytes/s write and 65MByte/s read performance.

After setting up a raid0 I excpected definately some better numbers.
To my surprise, the array behaved exactly like a single drive -
except it has twice the space. Theres no performance increase, not a bit. Tweaking the stripe size and some newer BIOS I got finally
40MB/s write and 70MB/s read performance.

Thats not bad, but I have already a good IDE raid and so my
expectations are high. The difference between SCSI and my old
IDE setup is not worth the $$ i had to spend for it.

I wrote Mylex. Maybe theres some enlighted tech that can help me.

What are your best HD scores ?
And what should I do with my array ?
 
i really got no experience here but i know at 2cpu.com the scsi expert is upaboveit and they have many threads about scsi performance issues

link

also there is a thread about xp offering poor porformance with scsi raid since you dont list the os i'm just throwing it out here seriously check them out

hope this helps
 
First off, if you were running Raid 0 you should have seen a pretty substantial increase in performance...something isnt righ there.

Second, SCSI doesnt always mean faster than IDE. What you pay for when you buy scsi is:

Faster Seek times due to increased RPMS...the seek times on that 15k drive should be very good. Compare that to an ide drive and you will see a big difference.

Better quality product. Most SCSI equipment is warrentied for 5 years.

Less CPU utilization during heavy read/writes. Though IDE is getting better also.

Furthermore, on a 32bit PCI bus a u160 card with only 1 HDD is complete overkill if you ask me. That drive will never reach the bandwidth of the PCI bus, which by the way is less than the 160mb/s that the SCSI bus itself can handle. Thus the PCI bus will be saturated before the scsi card..which will limit it to less than 160mb/s. A decent LVD card is still a good deal and sufficient for the average joe wanting good performance out of scsi.

Even with your two drives the u160 card would never reach its potential.

The beauty of scsi is the onboard controller. Before the days of Burnproof on IDE you could never have done the things you could with SCSI. Like burning a CDR, ripping a CD and playing Quake at the same time. An IDE drive would have produced a coaster...

 
I have a question....why do people set up scsi raid '0' arrays with 2 drives that perform @ completely different levels?
 
The Compaq 15K drives that I had were both original version X15, and considerably slower than the 36LP that I have now. Many raid controllers offer excellent fault tolerance and rather poor striping performance. A great performer would be AMI Elite 1500 or 1650 ifn ya want to spend a lot of green, or mid level priced ATTO UL3D or even the UL2D performs much better in stripe than the average RAID hardware controller that I have had. With ATTO benching and 4 drives in stripe on a dual channel ATTO UL2D I get read and writes up to 143 synchronous MBPS. I have a UL3D coming and I can update on any improvements it may offer when I get it.

With the typical raid controller in the average users price range however it is not uncommon at all to see single drive performance, especially if using only a single channel. Also generally speaking a boot array will perform somewhat slower than a striped logical drive. Ive hit around 150MBPS synchrounous that way with the dual ATTO. Also if your controller is seeing those drives as 80MBPS drives, it is a U2W controller, not U160
 

Thanks for the link, Wolfsraider.
I will do some more research on the net.

Even if the benches are not convincing the SCSI setup is a lot faster
in a virus scan than IDE. Sandra came up with only 27000 points.
Sure I cannot saturate the U160 bus with only 32Bit,
but for now I would be happy if I could max out this PCI bus.
The next bigger upgrade will come and then I might consider 64Bits.

Flokster, what do you mean with different levels ?
The drives I use are comparabel but not identical.
If it would give me some performance I would also put my floppy into the raid 🙂 but the seektimes would mess up everything.
 

I have also been looking at ATTO, but it happens the
Mylex was a cheaper deal at ebay and there I have not seen
any ATTO. Maybe the people are happy with them.
Mylex has also a good reputation. I'm not sure whether it is
the controler or one of the harddrives that causes the problems.
Seems like I have to figure it out the hard way.
 
THe ATTO RAID solution kits are hard to find on Ebay, or just about anywhere used. I have been in the hunt for the UL3D raid kit for almost a year... and yesterday I finally scored 🙂 It may seem expensive but its less than half the lowest price on PW

Its an open box return and the seller neglected to mention it was the raid solution kit, or that it is PC compatible, and I just happened to run my search about 4 hours after it listed. The search engines dont show up new stuff for a couple hours so I stumbled upon it by luck. You can find the UL2D fairly often but you have to be carefull to get the true dual channel controller, not the single channel on a dual channel HBA OEM MAC version you see most of the time there. It takes a lot of research to find what controller will best suit your needs and time and luck unless you want to pay retail.
 
I haven't done my homework lately but are the 2 drives you're using the same? are they both 80pins or 68pins? Just make sure your connectors are up to par with your drives. Sometimes cheapy connectors lowers your throughput. I have a RAID 5 at work and its much much faster than any IDE drives I have ever used (simply no comparision). 🙂


--Scsi
 
For RAID (especially a striped pair) the drives need to be identical down to the firmware revision! ANY deviations can result in strange behavior or even data loss!

Cheers!
 
Congrats mastertech. You had a really long breath and patience has paid. Wish I could play a bit with your rig.

I have one drive connected with SCA adaptor and one directly.
Most people recommend to stay off such adaptors.
The controler reports both drive as U160 and as single drive they work well. I thought the bandwidth is fixed then ? Can the transfer rate drop during access due to bad cables ?
 
For what its worth I have one 2nd generation 18Gig X-15 on an Adaptec 19160 and get bench scores of +60MB/s on both read and write, switching to this from IDE was like night and day.
 
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