I recommend the Highpoint X4 external 4 bay (removable) with their RocketRaid 2322 PCI Express SATA II controller. That card takes one 4-lane PCI-express slot and hosts up to two external enclosures with Infiniband. The real value of this card is that it uses on-board formatting and make RAID 0-1-5 and 10 available. Typically when using the Apple DiskUtility to RAID disks into a set, they are setup by the operating system and it is very easy to loose that setup when updating the OS. With the RocketRaid card, you never loose the RAID set.
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