Buyer's Guide: eSATA Enclosures
This page covers recommended eSATA(external SATA) enclosures.
Please note that external SATA (eSATA) drives/enclosures are generally not bootable, and that putting the machine to sleep does not sleep the external enclosure or its drives. There is one appealing workaround on a Mac Pro: the NewerTechnology Extender Cable, connected to the two unused internal SATA ports (this will sleep the drives, but not a fan, if present).
If “sleep” is a requirement, then your choice is Firewire 800. It won’t offer the best performance, especially with a dual drive striped RAID (or even a single drive), but when the application is something like a Time Machine or other incremental backup, raw performane won’t be an issue once the initial backup is performed.
Your best choice for the ultimate in flexibility is a “quad interface” enclosure, which supports eSATA, Firewire 800/400, USB 2.0. There is a downsize to such flexibility: the “bridge board” used to provide it slows eSATA performance by about 4-7%. For systems where eSATA is to be used exclusively, choosing an enclosure with eSATA (only) means the highest possible performance.
Adapter cards for eSATA (Mac Pro or MacBook Pro)
Most of the enclosures on the market supporting more than two drives use port multiplication. Port multiplication is fine for many uses, but it is not a high performance solution because the use of a single eSATA cable throttles the maximum speed. Even just two hard drives can show reduced performance over a port-multiplied system.
Hot-swappable choices PERMALINK
Hot-swappable enclosures utilize drive trays: the drives are screwed into the trays, and can then be inserted and removed at will while the device is powered on, though you of course must unmount any volumes before removing the drives.
For mirrored RAID, drives can be yanked out at will (leaving at least one mirror drive intact), and this is one odddball means of creating a backup: you can add the new drive to the existing mirror and let it rebuild the mirror on that drive, so long as the system is not actively modifying the mirror volume.
The FirmTek SeriTek/2EN2 and SeriTek/2eEN4 enclosures (2 and 4 drives respectively) offer hot-swappable drive trays, these are also available at OWC. These enclosures are somewhat more expensive, but allow easily swapping as many hard drives as you want, each in its own tray ($24 each or so). Install your own drives, and buy as many extra trays as you need. A swappable solution can be very convenient for users with many different project each requiring its own storage.
I make rotating backups with external sets of hard drives screwed into FirmTek SeriTek drive trays. However, given the cost of the trays, it will be about as cost effective to just buy as many of the OWC enclosures as you need—the enclosures costs only slightly more than the FirmTek drives trays. In short, hot-swappability might or might not be a requirement if all you want is multiple sets of drives.
Some enclosures screw the drives in; installing new drives means unscrewing the old ones and screwing in the new ones. Other enclosures use drive trays, and might even be hot-swappable.
OWC offers a range of external enclosures. The most flexible are the quad-interface versions (eSATA, FW800, FW800, USB), but you can also go with straight eSATA.