SCSI Array Configuration

azev

Golden Member
Jan 27, 2001
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Let say you have dual channel U160 controller and you are have building external drive array of 10 U160 15K IBM drives.
Is it better to connect one channel to all the 10 drives or have a split backplane of 5 drives and connect each channel of the controller to each backplane ? I am going to create one raid 5 array with speed/redundancy as the primary goal.
I have the controller and the drives, so if you guys have any suggestion please just throw it in.
Btw, since each of my controller channel have the bandwidth of 160Mb, if I use both of the channel and create only one array I'll get theoratically 320Mb bandwidth, am I correct ??
 

sharkeeper

Lifer
Jan 13, 2001
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It is always better to stripe across channels then down them. In the high end realm of 15k U320, just four drives is the practical limit per channel.

-DAK-
 

azev

Golden Member
Jan 27, 2001
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So basically I would get better performance by having 3 channel raid controller and connect 3-4 drive on each controller and then create one big raid 5 array ???

Or maybe get a dual channel U320 raid controller ????
 

sharkeeper

Lifer
Jan 13, 2001
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You would start to see interface bottlenecks with more than six drives on a dual channel controller, although it's not necessarily bad. Ten drives on one channel would be bad.

-DAK-
 

azev

Golden Member
Jan 27, 2001
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Would getting a controller with faster interface such as U320 for a U160 drive will help eliminate the controller bottleneck ??

 

sharkeeper

Lifer
Jan 13, 2001
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Yes but remember that the drive's begginning STR x number of drives should be < = 90% of limit of interface or you'll hit the wall.

-DAK-
 

azev

Golden Member
Jan 27, 2001
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the drive's begginning STR x number of drives should be < = 90% of limit of interface or you'll hit the wall.

I am sorry, I dont quite your last statement, would you mind to elaborate alittle ?

Thanks
 

charlie21

Senior member
Oct 10, 1999
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I believe that shuttleteam's trying to say that if the combined maximum sustained transfer rates of the drives on a channel exceeds 90% of the channel's maximum theoretical bandwidth, then you'll hit a bottleneck there.
 

sharkeeper

Lifer
Jan 13, 2001
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Yes that is correct.

Many servers running databases will use small stripe sizes so the STR bottleneck isn't so bad with many drives. The Enterprise class HBA's seem to show this pattern. For workstation use, larger stripe sizes of 64KB and higher are recommended for this reason.



-DAK-