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I have some questions about raid card.

Use LSI MegaRAID® SAS 9260-8i raid card as a example.

There is only two connection ports on the raid card, and they provide two cables that can connect 8 SAS/SATA storages. The document say it can connect "Maximum 32 drives per controller", I want to know how can I connect more than 8 hard disks with this card.

Is that they say "Eight internal SATA+SAS ports" means they provide two cables which can connect 8 hard drives, but you can use other way to connect Maximum 32 drives?

The other question. I see host bus adapter has raid integrated , so what is the difference between host bus adapter and raid card. Are they the same?

I also know is SAS/SATA Expander's function only to connect more hard drives?

Thanks in advance.

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2 Answers 2

up vote 2 down vote accepted

This is easier than it seems, and you're already onto the solution.

Basically it has two channels of 6Gbps each, each connector can have a 1-into-4 cable pugged into it going off to either a single drive or an expander, each expander capable of supporting 0-4 drives. This is how you'd get to 32 drives, through the use of expanders.

Oh and at its simplest a HBA converts back and forth between the system and its disks while a RAID card does the same but more - it lets you bunch up disks into virtual disks of various types of array (R0/1/3/4/5/6/10/50/60 etc).

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Just to add a note. There's no such thing as a SAS/SATA Expander. There are SAS Expanders (which also will run SATA drives, but require a SAS HBA), and there are SATA Port Multiplier (which only work with SATA equipment). Also, I've seen SAS Expanders that support up to 32 additional drives (but your HBA has to support that many). Also some manufacturers list the maximum dives based on using their hardware only, if the card used 3rd party expanders sometimes you can get more drives (obviously not supported). Also the raid ability of the card will only support XX many drives. –  Chris S Jul 9 '10 at 12:41
    
I didn't say there was, that was in the original question. –  Chopper3 Jul 9 '10 at 13:03
    
I want to ask more. For example, I'm using a raid card to build raid 5. Can I add another raid card, and combine those hard disks connected to this two raid cards to one larger raid 5 disk? Is that I can use the second raid card as a expander and don't use the raid function of the card, just use first raid card's raid function to achieve? –  cpps Jul 9 '10 at 18:53
    
@cpps, almost certainly not - as far as I'm aware arrays can only be owned by one controller - I don't quite understand the second part of your question. What is it you're trying to achieve? let us know and we might be able to help ok. –  Chopper3 Jul 9 '10 at 20:31
    
My second question is that can I treat the second raid card as a expander and disable the raid function of this card, then let the first raid card control the hard drives of the second raid card, is this work? In addition, can you tell me we should use two raid card together in what situation? For backup of the another card in case the other card is down? –  cpps Jul 9 '10 at 21:00

Yes. having two RAID cards is possible in one server. combining the RAID cards is not possible. Best practice does not recommend to have two seperate RAIDs in one server. Hence, if you want to have a large LUN then better is to attached a DAS (Direct Attached Storage) to the server.

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