Quorum drives

[chiph]

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I was looking at one of the sample configurations in the Netfinity configurator, and IBM was using a fibre channel RAID adapter that had a mirrored set of quorum drives. What are quorum drives used for?<br>
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The actual configuration shown was: 8 Netfinity model 7000M10 servers redundantly connected to two fibre channel hubs, each of which was connected to a fibre channel RAID controller (also redundant), and each RAID channel (6 in total, 3 per controller) was connected to a EXP15 drive chassis. There were a total of 58 hotswap 18.2Gb drives, with two more dedicated as quorum drives.<br>
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I'm not thinking of building one of these terabyte monsters, just curious. Thanks for any help.<br>
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Chip H.<br>

 

[chiph]

To answer my own question:<br>
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Quorum drives are used in clustering implementations to determine the cluster configuration. Whichever machine has possesion of the quorum drive is the master, and is "in charge". If one of the other machines in the cluster determine the master is no longer responding to client requests (via a "heartbeat" network request being unanswered, or other means), it will issue a SCSI or Fibre-Channel reset command, and if the master doesn't assert itself in a fixed time period (typically 10 seconds), the non-master machine in the cluster promotes itself to master and takes control of the quorum drives. Processing resumes. In Microsoft's implementation, any uncommitted database transactions will be lost, but other implementations (Tandem? Compaq/DEC?) don't have this limitation.<br>
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Quorum drives are typically mirrored for redundancy, whereas the other "storage" drives are usually RAID-5.<br>
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Chip H.<br>