No experience with these drives, I'm afraid (though they look fantastic). How is the drive appearing in Windows? Is it a mapped network drive, for example?
My guess is that unless it appears as a volume in Disk Management then 844/X isn't going to be able to connect. But again, that's *not* experience talking. Have the Isilon support people been able to help?
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As far as I know one way the 844/X decides if a drive is fast enough for video capture is that it only looks for drives connected to a storage card (e.g. SCSI) that is placed in a special slot on your CPUs PCI bus. Are the drives connected to the same card as your other storage? Or did you add another storage connection card, like a SATA card? If yes, try placing this card in the slot where your SCSI card is now.
And make sure that your drives are formatted correctly.