Dual Channel SCSI

[Brad4321]

Now that my dually opteron system is running, it is time to get my raid array doing the same. Upon looking at the price tag difference between single and dual channel scsi controller cards, I figure that I better make sure I know that I can use the dual channel one fully first.

How much data needs to be transferred at one time/simultaneous access to saturate a single and dual channel cards? I have close to a TB in IDE drives now, which I will be slowly transferring over to my new scsi array as I add more drives for it. Around 2TB is my goal at the moment (which will rise once that gets full). This equals a lot of drives.

I was looking at this controller card, but I am open to suggestions, PCI-X cards that support at least raid 5. Since the card allows 15 drives per channel, is it truly possible to put 15 drives per channel? I didn't think they may cables that complex. If they do, I would figure that it would be pretty easy to overload that configuration.

Serial SCSI? Is Ultra640 the same as serial scsi? From the way it reads, this isn't out in the market yet. They said drives would hit the market the second half of 04. Well, we in the middle of that and I haven't heard a single thing yet. Are the benefits worth the wait?

No, I'm not done yet .I was thinking of getting a couple of 15K drives in raid for my OS and program installations, and 10K drives for my frequently used files, then keep all of my old 250GB SATA drives laying around for my static file storage. Is it possible to have 2 different raid arrays on a single card? I would put the 15K drives in a separate array than the 10K drives.

As you can tell, I haven't used scsi before. I am looking for the max performance and reliability that I can get, so I am open to suggestions.

 

[aug1516]

How much data needs to be transferred at one time/simultaneous access to saturate a single and dual channel cards?

That depends on what type of SCSI card you buy. If you buy a single channel U320 card then you would need your drives/array to use up to 320MB/sec of bandwidth to saturate that channel. If it's a dual channel U320 card then you would have 640MB/sec of bandwidth available if the drives were split up between the two channels. You will have to do some research on the specific drives you are looking at to see how many it would take to saturate a single or dual channel U320 card. The Fujitsu MAS3735 (15k SCSI drive) has been benchmarked at a maximum speed of 78.6MB/sec during read sequential transfer operations in the outer-zone of the disk. So if you had 4 of these drives and they all happened to hit 78.6MB/sec at the same time (very unlikely), you would have used up around 314MB/sec in bandwidth. In theory, if you added a fifth drive you could actually saturate the entire 320MB/sec of bandwidth available. I would head over to storagereview.com and look up the benchmarks on the drives you are interested in. That should give you some idea of how many it would take to saturate an U320 channel. Just remember that even if the drive is capable of high read speeds it is very unlikely that all 4 or 5 of your drives would reach that speed at the same time.

I was looking at this controller card, but I am open to suggestions, PCI-X cards that support at least raid 5. Since the card allows 15 drives per channel, is it truly possible to put 15 drives per channel?

U320 SCSI actually has a limit of 16 devices per channel as long as the cables are kept below 12 meters in length. Of course the SCSI controller counts as a device on that chain leaving you with 15 drives possible. That card you linked only supports Raid 0, 1, and 10. I have not used RAID 10 before but I know that RAID 5 is probably one of the most popular RAID options if you want performance and data redundancy, may want to look that way.

Serial SCSI? Is Ultra640 the same as serial scsi? From the way it reads, this isn't out in the market yet. They said drives would hit the market the second half of 04. Well, we in the middle of that and I haven't heard a single thing yet. Are the benefits worth the wait?

As far as I know, U640 SCSI is just another step ahead in the quest for more bandwidth; it is not the same thing as Serial SCSI. They usually implement some new technologies with each new SCSI protocol but the main advantage here would be doubling the bandwidth available from current U320 cards. I would not worry about waiting for U640 SCSI technology to become available; U320 should be enough for what you are doing.

I was thinking of getting a couple of 15K drives in raid for my OS and program installations, and 10K drives for my frequently used files, then keep all of my old 250GB SATA drives laying around for my static file storage. Is it possible to have 2 different raid arrays on a single card? I would put the 15K drives in a separate array than the 10K drives.

That also depends on the SCSI card. The higher end dual-channel RAID cards usually support multiple arrays, one on each channel. I don't know if the Adaptec card you listed will support that. You would have to dig into the specifications some more to find out. If you are really serious about a stable and fast SCSI Raid setup I would look at some more expensive SCSI raid cards that support RAID 5. One more thing I forgot to mention earlier. Make sure that your motherboard has PCI-X or PCI-Express on it if you are going to get a high-end SCSI array going. Standard 33mhz PCI slots only support 133MB/sec of shared bandwidth across all PCI devices. So your U320 card would never be able to reach its full potential, or even half of its potential in a standard PCI slot.

 

[UICompE02]

Serial SCSI? Is Ultra640 the same as serial scsi? From the way it reads, this isn't out in the market yet. They said drives would hit the market the second half of 04. Well, we in the middle of that and I haven't heard a single thing yet. Are the benefits worth the wait?

Serial Attached SCSI (SAS) is not the same as Ultra640. You will not see Ultra640 SCSI, most likely. The signal issues at the speed are too complex, so the industry is moving toward a serial standard. 3.0Gb/s SAS controllers and drives will be available by the end ofthis year. Is it worth the wait? Well, for your application, I'd say probably not. I don't think you'd see enough benefit to justify the initial high costs of a new technology such as this. Plus drives will be hard to find for the first few months after they are publically released.

You can attach 15 drives to a U320 SCSI controller with no problems. The only hard part is finding a cable like that. Typically, applications that require 15 target drives use an external enclosure box that will have 15 drive bays and a single SCSI connector to go to the controller. You could also do what I do in our lab - make youre own 15 device cable. But that could be quite expensive as you have to buy the cable and connectors seperately.

The controller you have linked to does not support RAID 5. That only allows RAID 0 and 1. Might I recommend something like
this for single channel , or this for dual channel.

 

[Lazn_Work]

That also depends on the SCSI card. The higher end dual-channel RAID cards usually support multiple arrays, one on each channel. I don't know if the Adaptec card you listed will support that. You would have to dig into the specifications some more to find out. If you are really serious about a stable and fast SCSI Raid setup I would look at some more expensive SCSI raid cards that support RAID 5. One more thing I forgot to mention earlier. Make sure that your motherboard has PCI-X or PCI-Express on it if you are going to get a high-end SCSI array going. Standard 33mhz PCI slots only support 133MB/sec of shared bandwidth across all PCI devices. So your U320 card would never be able to reach its full potential, or even half of its potential in a standard PCI slot.

I have yet to see a card that supports Hardware RAID 5 and does not support multiple arrays, even single channel cards. (I have several servers running multiple arrays on a single channel)

And if you are serious about RAID, get a hardware RAID 5 card.

==>Lazn

 

[Ice Czar]

hmmm...since no one else asked, application and environment?

what access pattern are we talkin about here?

 

[aug1516]

hmmm...since no one else asked, application and environment?

what access pattern are we talkin about here?

Since when did usage become important around here? It's not important why someone needs a 15k SCSI array, just accept that they do.

 

[Ice Czar]

LOL

then how can you tell your squarely in the overkill zone?

(says the mod with 2 SAN w\ 40 SCSI HDDs at home)

 

[Dark Ember]

LOL

then how can you tell your squarely in the overkill zone?

The the hell is that? Never heard of it...

 

[Brad4321]

Of course it is an overkill. This is [H] after all . I need something to complement my dual opterons, which has PCI-X for those who asked. The .1 seconds faster that 15K atlas's in raid 5 open large photshop files compared to raptors in raid 0 will surely be noticable by the masses , as per a review I just read.

hmmm...since no one else asked, application and environment?

what access pattern are we talkin about here?

The environment is everything, as I tend to play with everything except macs.

Continuessly accessed for at least 50% of the drives 24 hours a day. At least that is what I am averaging now.

Typically, applications that require 15 target drives use an external enclosure box that will have 15 drive bays and a single SCSI

I was hoping I could buy those cables premade, as I already have the enclosure.

It seems that I won't be able to saturate a 320 dual channel now, but if I keep adding drives as I plan to, I will in the future, so I am looking at those still.

Might I recommend something like
this for single channel , or this for dual channel.

That chip is for normal PCI slots. I would suppose that this is the same thing, just the pci-x version?

It seems as though it is a very well praised and performing card. Although half the cost of my current system, it will probably be worth it.

 

[Ice Czar]

The environment is everything, as I tend to play with everything except macs.

Continuessly accessed for at least 50% of the drives 24 hours a day. At least that is what I am averaging now, as I already have the enclosure..

so, a single user environment, well dual channel U320 would certainly be overkill
but as you said this is the [H]ard

 

[MrDigital]

You could always go with Fibre Channel if you want something unique and relatively expandable more so than anything else. The good news is that you can find FC drives on ebay for extremely cheap (compared to new) since very few people can actually use them.

It's no faster than U320, but it's definitely neat.

I'm also going to say there's very little chance you saturate an U320 channel... no matter what type of array you run. There's a big difference between accessing 50% of your drives and accessing 50% of your drives at 100%.

My RAID-0 array is capable of 119MB/s according to Sandra, but is that anywhere near plausible in any situation? Doubtful.

SAS is very nice too, if you want to wait for it. I'm definitely switching out my drives to SAS when it comes out if only because the cables are the same as SATA and it will get rid of one of the few remaining large cables in my PC.

-MrD