Regarding your response titled "More on RAID", you said, "So, if you use dual adapters you can survive a link failure and also get great performance."

Are these dual adapters, when in ongoing operations, both active at the same time (providing the total bandwidth of two adaptors) or is one of them in stand by mode?

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Depending on the "path management" software used to provide this functionality, they are usually active/active connections rather than active/passive. Most of the leading vendors use active/active. Load balancing metrics can be based on queue depth to the port or use a round robin method or both. Failover is automatic and usually there is automatic failback when the path is fixed.

Most path failover software supports up to eight adapters per server so you can aggregate bandwidth using 2Gbit HBAss to around 1.6 GigaBytes per second on a single server (the storage array must be able to feed at that speed though). Of course, your server must have a robust PCI architecture to support those speeds also.

I have done testing on the large Sun servers using Veritas or Solstice Disk Suite to spread the back end I/O load across multiple paths, and we have seen in excess of 77000 IOPS using only four adapters.

Chris

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Editor's note: Previous Ask the Expert response this question refers to: http://www.searchStorage.com/ateQuestionNResponse/0,289625,sid5_cid451331_tax286192,00.html

This was first published in March 2002

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