SCSI Backward Compatibility

[2Whyzzi]

I've got an older server here where I work and want to upgrade the SCSI hard drives that are inside it. They are attached to a Caching SCSI Ultra2 controller card that has 32megs of RAM on it (Mylex Extreme RAID 960/1164).

I've been told from my suppliers that all they can get are SCSI Ultra320 drives in. From <a href="http://www.maxtor.com/en/technologies/u320_interface/index.htm" target="_blank">this page</a> on the Maxtor website suggests that Ultra320 are backwards compatible with Ultra2. So thats the theory, what is the result in pratice?

Many thanks in advance,
2Whyz

[Wombat]

Yeah, they should slow themselves down to Ultra2 speeds. The only real danger is that you can't mix HVD (high voltage) and LVD (low voltage) parts, but I don't think you're at risk for that.

But you might want to check with another supplier. Ultra320 carries a price premium over older Ultra160 drives, and you're not going to see any difference in your rig.

Get a new SCSI card, or go get an older drive off eBay.

[Taz]

You may also need to force the drives into Single Ended mode, there's usually a jumper to do that

[2Whyzzi]

Would there be a big performance difference upgrading to a higher performance SCSI (Ultra 320) card over the caching controller on a BX-Pentium3? Likely stuck with 32bit PCI... (I haven't checked over the mainboard specs, but I do know the chipset is a BX).

Thanks again ppl.

[UtwigMU]

Depends:

Current 15k Storagerview 15k leaderboard drive has a transfer rate between 78,6 and 64,1MB/s

SCSI U2W can take 80MB/s so 1 drive would saturate that.

If you plan to use 2 drives concurently, there would be gains from faster controller, but SCSI 160 would be enough for 2 drives. Test out performance first. If you see bottlenecks (drives not outputing what they physically could), get a used or new 160 card.

[2Whyzzi]

Actually I'm not planning of concurrent usage, only mirroring (raid lvl1).

[Wombat]

That IS concurrent usage.

[VJ]

As far as backward compatiblity goes, I have run an IBM UltraStar 36 lzx (68 pin, U160) from an Adaptec 2940UW without problems. (<- this was temporary, I'm now running an U160 and a U320 on a U320 onboard controller)

As Taz mentioned, there is a jumper to force SE mode.

Note that LVD drives never have onboard terminators, so you need a cable that has a terminator.

Jörg

[Ribbit]

BTW, you shouldn't normally need to force SE mode in any case - the LVD devices should auto-detect it.

[Taz]

Originally posted by Ribbit
BTW, you shouldn't normally need to force SE mode in any case - the LVD devices should auto-detect it.

Should and does are very different things

[2Whyzzi]

I suspect the hot-swap box I'll be putting the new drives into would be self terminating (the box, not the drives). Although I an sort of wondering how I am going to set the SCSI IDs, the seagate ultra320 cheetahs (lw) I recieved are bare drives only, and they don't look to be like standard jumper connectors (ie use motherboard std jumpers).

[Ribbit]

They might auto-set the IDs themselves. Look up something called SCAM.

[KvHagedorn]

You're getting a hot-swap box and LW series drives? :buzzer:

Doesn't the hot swap box have a backplane which takes 80 pin hot swap drives? If so, you need LC series drives in there. LW series are 68 pin with separate power plugs. With those you need to set the ID and terminate the cable at the end. My backplane sets the IDs automatically (as I remember I could set a jumper and get another series of 5 IDs.) I have an ElanVital (Asus) backplane.

I've never had an issue running newer scsi stuff on an older controller. I have u320, u160, and ultra2 drives running concurrently on my backplane which is hooked into one channel of my Ultra 2 dual channel scsi controller. All the drives are LVD (LC series Seagate.) That channel runs as fast as the controller will allow. The other channel handles the CD-ROMs. This configuration is pretty simple, but you do need a second channel for the SE stuff (50 pin legacy scsi) or everything would work in SE mode. Not sure if LVD drives would even do that since I haven't tried it, but it sure would slow things down considerably even if it did work.

[VJ]

What KvHagedorn said...
I use a 2940UW (ok, it is overkill, but it is the only one I have lying around; grew historically) for my slow devices: scanner and zipdrive. All my other drives (U160 and U320) are connected to my onboard U320 controller).

Also, most 68 pin drives have different 'jumpers': one located at the back (between 68 pin and powerplug), where you can set SCSI IDs, and other information. There usually is a second set of pins near the front (and mostly on the bottom side). On these set of pins, you can't use jumpers, as a number of pins are combined. Some cases (or hotswapboxes) have a cable that fits on these pins. You can then set the SCSI ID on the case (as well as other information).


Jörg

[2Whyzzi]

Originally posted by KvHagedorn
You're getting a hot-swap box and LW series drives? :buzzer:

Doesn't the hot swap box have a backplane which takes 80 pin hot swap drives?

Oh You are most definately right in this case. I took the empty clips out and peered inside, definately 80pin anchors there. Looks like I made a mistake (and that is putting it politely). Oh well, I have a way around it - I made sure there we picked up an Adaptec 29340A-R.. and fortuneately the case has 2 spare 3.5 drive bays I can put them in.

Back to the old addage: Look before you leap. That, and offer up any and all information into a forum thread that might the difference when looking for an answer!

The drives we got only cost us $226cdn for 36gig. I thought that it wasn't that bad for Ultra320 compatible drives.

Thanks for all of the input ppl.