I am attempting to educate myself on SCSI raid, so far, so good.

I have come across a stumbling block however.

I am checking out several SCSI raid cards, I have determined that (for good performance) I am interested in:

64-bit
expandable on-board memory module
U160

With that in mind, I found a few that fit the bill, by LSI Logic, Adaptec, Mylex, and ATTO.

What I dont understand:

1) What is the difference between 1 channel and 2 channel? For a 2-disk RAID 1 array does it matter? At least with IDE, you would get max performance by using 2 different channels as opposed to master+slave combo, but of course SCSI works differently. Help!

If my hypothesis is correct.. how much loss of performance are we talking about with just 1 channel RAID-1?

2) These memory modules on the adaptors.. are they just standard PC133 ECC registered ram? I cant tell from the photos. They look shorter to me, like the old EDO ram :)

3) Adaptec makes a raid add-on card for motherboards with built in U160 SCSI. They call it 0-channel RAID. What do you do with that? I do not currently own such a board so I have no idea where it might plug in / how it works. I did understand that it turns your U160 onboard SCSI into RAID somehow...

Thanks for helping a newbie out!

Two channels means two separate u160 chains. Scsi works the same way. 4 cheetah 15.3's in raid-10 can really move some data! imagine 8 on that chain. I would probably keep 4 cheetah 15.3's per u160, or just move to u-320, it has some extra features that come in handy. One drive will never fill u-160 bandwidth im afraid to say.

2. Adaptec uses ecc simms last time i checked. the 256mb simm really helps out alot! newer adaptecs (2100/2200s have 64mb embedded with no expansion).

3. 0 channel raid is pretty cool when you have a nice serverworks motherboard. You have U320 on the mobo already, just use it, and the card abritrates the rest. Cheaper, and smaller size board (as in 2u fitment).

ultimately you need to think about your raid strategy more. Two drives in raid-1 isn't probably gonna be that much faster than IDE. When you hang 8-16 drives off that U320 2 channel raid controller on a 64bit/66mhz mobo, you will start to see unreal disk io performance (raid-10 of course).

I have some 4x180GB (16mb cache) 7200 barracuda's and those u320 cheetah 15.3's in 4x73gb (8mb cache) are really 2x faster and then some.

Serving mostly static content, a p3-xeon-550 can probably push 45mbits sustained spread over 300Gigs of html without breaking a sweat, so yeah, it is all in the bandwidth.

If you ever notice your loads are getting high, but you have high cpu idle time, thats a darn good sign that your disk subsystem is bottlenecking as long as you aren't swapping (which a webserver should never do, ram is cheap).

Take a look at the adaptec 2100S or 2200S line, they are really fast, U320, all that good stuff. Match them up with quads of cheetah 15.3 drives and i guarantee you will push some massive disk i/o bandwidth. Top notch stuff.

So you can have a single-channel U160 scsi raid card and do *meaningful* transfers that way?

I know raid-1 isnt much, I am just trying to educate myself at the moment. When I am ready to purchase, I am not sure I have the $$$ for 4x SCSI drives to do RAID 0/1.

I figured that this would be a far better setup than IDE regardless of configuration, based on seek times, drive durability, and future expansion capability (the reason for U160 instead of SCSI-2).

I am a lifelong IDE user trying to break free...

This is all concerning my upcoming, 3-server hsphere install, I want to make sure I do this right the first time.

Speaking of Raid 0/1... lets say I get a 2-channel card and 4 drives. Now, if a drive fails, I can hotswap it out, and then does the array build on the new fresh drive? If you have any more detailed info, URL's, etc I am all ears (eyes?).

THanks.

You should definitely look for SCA if you want hot swappability. Alot of the adaptec units will automagically start rebuilding once it detects a replaced failed drive. I know my 3410s does that. Didn't even have to tell it anything. Just started its thing. One of the 180GB drives i got, failed a few minutes into newfs'ing so i just had to go through this. Performance in raid-10 is not degraded of course when a drive fails thank god ;)

If you're interested in hot swap, by all means buy a chassis that holds SCA hot swappable drives, helluvalot easier than just mounting them up using 68 pin scsi and having to tear it apart when a box fails (thus not really hot swappable).

Also make sure your Version of linux supports the raid controller, and by supporting it means non-beta. don't want a fresh new buggy driver for a spunky new card to rely on ;)

lol

Originally posted by rigor
ultimately you need to think about your raid strategy more. Two drives in raid-1 isn't probably gonna be that much faster than IDE.

That's funny. Let's move up to RAID 10 with 8 15.3 drives right away!

It's going to be much faster with two drives, even old(er) drives. The only IDE drive that comes close to matching a SCSI drive is the some of the 8Mb cache drives but they only match 7200RPM SCSI drives. Check out storagereview.com both of you.

Originally posted by rigor
...ultimately you need to think about your raid strategy more. Two drives in raid-1 isn't probably gonna be that much faster than IDE. When you hang 8-16 drives off that U320 2 channel raid controller on a 64bit/66mhz mobo, you will start to see unreal disk io performance (raid-10 of course)...

...take a look at the adaptec 2100S or 2200S line, they are really fast, U320, all that good stuff. Match them up with quads of cheetah 15.3 drives and i guarantee you will push some massive disk i/o bandwidth. Top notch stuff...


Four 73Gb Cheetah 15.3 SCSI drives? Eight drives? More than eight drives? Hell yeah, great choice for a someone just starting out (is my assumption on this correct innova?). Let's add to that dual 2.8Ghz Xeon's or perhaps the $10,000 2Mb cache CPU's that was suggested to me by rigor. Let's not forget 12Gb of RAM because it's cheap right rigor?. Another space saving idea (to save money of course) is one of the $600 1U chassis with four SCA trays. rigor know's 'cuz the "pays to play" Pentium 4 3Ghz, dual Xeons, more RAM than he know's what's to do with, fastest hard drives, best of everything for "research purposes" of course!

Sorry for sarcasm but come on rigor, if you're going to make a suggestion make something you think will actually help the person. Not just telling him what the top brands and top models are. He can already assume that.

Anyway, one channel is fine for your config. It doesn't need to be changed to RAID 10 with 8 hard drives or even 4 for that matter. I would suggest Maxtor's 10k III drives. The 18Gb version can be had for under $100 and performs as well to anything else. That is, of course, REAL WORLD performance not some damn benchmark. Yes the 15.3 drives are very fast but on a price vs. performance scale they're a bad choice, how do you think AMD can sell lower performing CPU's over Intel? Price vs. performance. And to futher my point, "lower performing" is on benchmarks not real world performance.

If your drive fails the server can continue to function with a failed drive with RAID 1 and will rebuild (and will be slow during the rebuild) once you replace the drive. Some controllers will even email you when it happens if you set it up to do that.

Adaptec ZCR is nice but I would go for an LSI Logic MegaRAID Elite 1600 2 channel card. It's expensive at over $700 new but you can get it on ebay for $220 with some nice addons like the battery and 128Mb cache memory upgrade included. The 2 channels will give you an upgrade path once the server is old so you could load the thing up with a bunch of drives WHEN YOU NEED TO if ever depending on the load of the machine. Only catch, you'll need to pick up some SCSI cables.

Hope this helps, good luck on your project.

Originally posted by innova
Adaptec makes a raid add-on card for motherboards with built in U160 SCSI. They call it 0-channel RAID. What do you do with that? I do not currently own such a board so I have no idea where it might plug in / how it works. I did understand that it turns your U160 onboard SCSI into RAID somehow...

There's two versions:

1) Plugs into a slot similar to the RAM slot on your motherboard. A good choice for a 1U chassis as it's nice and small.

http://www.supermicro.com/PRODUCT/MotherBoards/E7500/P4DPL-8GM.htm

See the white slot above the 64pin SCSI connector, that would be for a ZCR card.

2) Plugs into a regular 'ol 64bit, 66Mhz PCI slot.

Both come without any channels to plug drives into. Hence, "zero-channel RAID". If you have a motherboard with a SCSI controller built in that supports ZCR you can use a ZCR card to add hardware RAID ability and the card will use the channels on the motherboard instead of on the card itself.

It's pretty neat but in the end the cost of a motherboard with integrated SCSI vs. the cost of one with only IDE is enough that you could afford a card with it's own channels.

I don't have experience with ZCR but some folks around my datacenter I'm colocated with do and say it's great. So basically, there's a short rundown on ZCR but I don't know how well it performs.

Sorry to jump in and switch but:

Just to help a noob out what are some good linux systems that support raid.

Thanks

hmmmm.... yes i agree rigor's idea was overkill, but i think he was just giving an example of what he was currently using...this is a help forum Rags not a flame random ppl forum cause you think you more intelligent! either way i would stick with scsi over IDE any day for data and web servers, there are affordable scsi drives out there just go to www.pricewatch.com and you will find some great deals.

btw- Intel does make a better chip set all around, but if you going to build a personal gaming machine AMD is always the best choice for video!...just an opinion