SCSI Setup

[Crosstrack16]

Planning a new system (wont be ready to start for about a year) and i want two Seagate Cheetah 18.4 GB drives, U320 of course. I was looking for a controller card and i see two options, single and dual channel. I'm not sure which one to choose. As far as brands, i'm told Adaptec is up there. Any help in choosing a controller and setting it up would be appreciated... (raid configurations, etc.)
Explain it to me as if i were 5 yrs old.:shrug:

[bigben2k]

First off, Adaptec is the only way to go, IMO. It might be touchy on the clock rate, so if you're running a KT400x, you might want to look at something else. The main advantage is the reduced CPU load, and you just can't beat Adaptec for that.

U320 is too much, for a workstation. I've been looking at U160, and you know what? It's still too much!

Check out HDDs at www.storagereview.com and look for the data rates. You'll find that an Adaptec AH-2940-U2W will fit the bill just fine. Otherwise, you can do like me, and aim towards a AH-29160, which will run just about anything without any issues.

The trick with the 2940 is that there's more than one of them, and you really have to find the one that allows the 80 MBPS data rates, to accomodate the latest drives.

Are we skipping over RAID?

Have you looked at the prices of this stuff?

BTW, SCSI drives have a number of advantages. Do you know what they are?

[Arcturius]

Actually, you may want to look elsewhere for your RAID fix. I believe there are several competitors that beat Adaptec in that department. Take LSI Logic and Mylex, for example...
I can't complain about my AHA-2940UW, though.

Also, you may want to look at the IBM 15K drives, or some of the Maxtor(Quantum) drives, since price appears to be an issue.


Also, are you planning on running RAID 0 for streaming performance (silly, considering what a single SCSI disk can provide...) or RAID 1 for redundancy and increased read performance?

[Joe]

Theres a fact to remember ( and its lost on most IDE folks it seems )

U320 is power for a big array, it was built to accomidate the high data flows from massive arrays. U160 was choking with big arrays still.

An array to an IDE person is 2 drives 4 at the most ( 2 channels). To a SCSI guy 5 - 15 drives in a real array, 2 - 4 drives is just a few discs. With lets say 50 - 60MB/sec of physical read speed off a 15kRPM SCSI ( bestcase) you run out of bandwidth on the SCSI chain on a U160 with 4 drives (this is assuming 100% data use and no overhead, which never freaking happens). with U320 you can get 8+ drives working and loose very little data speed.

So... if you went with 320 you are doing it to get 4+ drives running. Otherwise I would recomend going with U160 goods. You still will NEVER EVER fill up a U160 channel with 2 discs.

And if you are going RAID, some Mylex is Ok, LSI is pretty good, Adaptec is nice, but pricey. There are some others but I would stick with those.

I currently have 3 36GB 10k/15k RPM drives ( one IBM and 2 Maxtor 8mb cache drives) in my workstation on a Tyan Thunder K7 using the onboard Adaptec dual Chan U160 controler (using only one chan) The streaming write speed is pretty damn impressive on all them, I dont think I need any hardware RAID for the machine since I dont see the benifit for the cost. Now on the other hand by the end of the summer I plan on upgrading to a new Dual Xeon setup on the Tyan Thunder i705 workstation board with the dual U320 SCSI and getting the Zero Channel RAID board upgrade for it.

My home server has 10 9.1GB 7200 and 10kRPM drives in it on 2 UW SCSI channels ( on a Dual Chan Mylex RAID controler), its nice, but I dont like Mylex much at all.

SO thats my lil thing about SCSI... I had SCSI in all my computers since I was like 11 or 12 I had SCSI drives and controlers in my machine for 6 years before I owned my first IDE drive. How I miss SE SCSI, all this LVD now... just not right hehehe

[Arcturius]

Joe,

Are you actually mixing drive models (and spindle speeds?!) in the same array, or did you build multiple arrays on the same controller from like discs?

I would also like to give an example of what Joe was indicating: four or more drives on a single U160 chain is fine, under certain conditions.
Small mail server, <10,000 users: Four 15K disks in RAID5 for swap and /var (mail spool) plus a pair of 10K OS disks in RAID1. In this example, I'm expecting the RAID5 to get hammered all day long (it's a mail queue, so writes are about as common a reads, possibly more so), while the RAID1 disks basically sit idle, since most everything on it that is useful hangs around in memory. Heck, throw on a CDROM and a tape drive (which rarely get used, and are slow even when they do...) and you're still probably below the ceiling for U160.

[Cova]

Be aware that if you want to run U320 (or even U160) you need pretty expensive SCSI cable too. Either of those speeds requires the twisted-pair 68-pin cables, and though they are cheap relative to the drives, after using $10 IDE cables all your life the price will suprize you at first.

For RAID, you can either go software RAID (striping in WinXP Pro, striping/mirroring/raid5 with 2K Server) or hardware RAID. Unlike IDE with fairly cheap "hardware" raid that is mostly done in the drivers (eg. HighPoint or Promise RAID as integrated on the mb) you will need to buy a real RAID controller for SCSI, which is again going to cost a lost more than a standard RAID controller.

I work with SCSI RAID all the time at work, and ran SCSI for a short time at home, but it's just too expensive and I went back to IDE. IMHO you're better off spending the money on other parts of the system - buy another GB of RAM to use just for caching the IDE drives and you'll probably get similar performance for less total cost.

[Arcturius]

The cables really aren't that expensive, if you think about it. You can get a cheap 9-position one with detachable terminator for about $45, which can accomodate 8 drives.
In IDE, it would take four cables to reach the same result, so you end up at roughly the same cost.

Plus, many SCSI cables are rounded by default, and since you usually only need one or two, they can really clean up the inside of your case.

[jtroutma]

Jess... I came in too late for this thread :P

Well I wil throw out my experince here just for the fun of it.

Currently, I am running (2) Seagate 36GB 15K.2 drives in RAID 0. As soon as I pick up an additional drive, I will be moving to RAID 5.
All of these drives are running of a single channel LSI Express 500 unit. I also have an Adaptec 131U2 and found that it wasnt worth crap! I bought the LSI off e-bay for a decent price and have been very satisfied with it.

Yes, U160 is more than enough for 2-3 drives.....4 begins to push the envelope (using 15K drives that is).

Let us know if you need any more information.

[Crosstrack16]

SO, to sum it all, i should opt for U160 in RAID 0 configuration using an Adaptec controller or similiar.

One other question though, just to make sure. I could use a single channel controller with both dirves on one cable, right?

[Joe]

Originally posted by Arcturius
Joe,

Are you actually mixing drive models (and spindle speeds?!) in the same array, or did you build multiple arrays on the same controller from like discs?

Yep multiple RPM drives in one array my home server is not what I would call a "model" of IT perfection. But that array has been running for 2 years now and there hasnt been one single error. so I guess the Mylex is tollerant of the different spindle speeds.

[Cova]

Yes - you only need a single channel unless you start getting quite a few drives. Unless you're doing video encoding or something and streaming huge files to/from disk (thereby reaching your disks max transfer rates) you should have no problems putting quite a few drives on a single channel. On all the servers we have at work we don't use a second SCSI channel unless we have to hook up a second SCSI enclosure (eg. 1 channel for drives internal, 1 channel for drives in external box). Besides the SAN (which is 6 channels, currently each with 13 10KRPM 36GB disks) I can't even think of a server we have that really makes use of a second SCSI channel (probably because all the servers that do that much disk IO are plugged into that SAN)

[Crosstrack16]

Thanks guys for all your help!!!

[Brad]

and of course you're probably going to be buying a motherboard with 32/33 pci, which has a real world transfer rate of around 80 - 115, depending on the chipset.