How many ports should I look for in a card for raid 5?

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I'm having trouble deciding between a 4-port and an 8-port card for a raid 5 array.

Since each port can connect 4 drives, my initial thought is that the 4-port card is all I need. (There's practically no chance my power supply could handle more than 16 drives.) However, what about performance? How does the signal multiplexing work for the 4 drives on a single port?

On a 4-port card, should I hook up 4 drives to the ports one per port? Or doesn't it matter?
If I might expand to 5 drives, should I be considering the 8-port card so that I can keep each drive for the array on a separate port?

Insight much appreciated, thanks!
 
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popatim
ports dont do any work. They just allow the drives to be attached.
In a hardware raid card, the controller does the work (the XOR calculations) which in turns controls the speeds you will see. Also some controller support an SSD cache drive which helps alot in buffering data & maximizing speed.

You want to start with 12TB (4x4TB) raid 5. Throw in a hot spare and an SSD cache and you've got 6 ports spoken for. Max size on a 2 port card would be 20TB (raid5) or 16TB w/Raid6 fwiw.

Unless you dont think you would fill 20TB, I would shop for a 4 port card. A 2 port card doesn't allow you enough expansion IMO without replacing all your drives. and an 8 port would allow you to at least double+
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I expect to start out with 4 x 4TB drives and grow from there. I'm not bothered with the slow write performance of raid 5, but would like to build the array with the best read speed I can have. I've chosen raid 5 for cost efficiency. The grey area for me is understanding how raid card ports work with multiple drives attached, so I can have the best raid 5 performance possible.
 
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popatim

popatim

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ports dont do any work. They just allow the drives to be attached.
In a hardware raid card, the controller does the work (the XOR calculations) which in turns controls the speeds you will see. Also some controller support an SSD cache drive which helps alot in buffering data & maximizing speed.

You want to start with 12TB (4x4TB) raid 5. Throw in a hot spare and an SSD cache and you've got 6 ports spoken for. Max size on a 2 port card would be 20TB (raid5) or 16TB w/Raid6 fwiw.

Unless you dont think you would fill 20TB, I would shop for a 4 port card. A 2 port card doesn't allow you enough expansion IMO without replacing all your drives. and an 8 port would allow you to at least double+
 
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