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Mixing SCSI Speeds on Smart Array controllers / devices

Regular Advisor

Mixing SCSI Speeds on Smart Array controllers / devices

Can somone tell me what the situation is these days with regards to mixing SCSI device speeds in various situations?

I used to think that, if you added a "slower" drive to an array, the whole bus would slow down to that speed (e.g. adding Ultra2 drives to an Ultra320 array) but reading an older quickspecs recently (which I unfortunately didn't bookmark) gave me the impression that this wasn't the case.

Specifically I'm interested in what happens on a 4314R enclosure (which I have myself and wish to populate with more drives), but I'm also interested in what happens with an MSA1000 (which we have at work and would like to re-utilise old drives unless they sacrifice performance on the others.

In short, if I have some Ultra3 disks in the 4134R and later add some Ultra2 disks (probably to a seperate Array to keep like-for-like disks in each array) and wondered if it would slow down the whole system to Ultra2 speeds?

Any feedback / pointers would be appreciated.

Steven Clementi
Honored Contributor

Re: Mixing SCSI Speeds on Smart Array controllers / devices


As far as I know, your performance will only be as good as the slowest drive... but you probably know that already.

So in effect, even if the rest of the "faster" drives are running at their normal rate, your i/o still suffers since the rest of the faster drives can't do anything until the slower drive completes the process.

Now, if you were to use slower drives ONLY in a separate array, then it should not matter too much since your I/O is not dependant upon a mixture of slow/fast drives.

If you can take it a step further and split your different drives across the 2 buses in the 4134R (assuming you may have meant 4154R), then effectively... you will split the drives on 2 different channels of an array contrller giving you the possibly of not efffecting the i/o of the fastr disks at all.

As for the MSA... it is U160 genetically so there isn't too much different if you use U2 drives vs U3 or U320 (The U320's are runnign at 160 anyway).

Steven Clementi
HP Master ASE, Storage and Clustering
MCSE (NT 4.0, W2K, W2K3)
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