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Promise Pegasus J4 — Recommended Configuration
Related: backup, Carbon Copy Cloner, cloning, hard drive, RAID, RAID-0, SSD, storage, Thunderbolt
Tested on the 2.7 GHz MacBook Pro with Retina display, which has a Thunderbolt connector.
Update: see issues.
Speed without safety is a dubious tradeoff. Yet backups are often skipped from inconvenience. How then to ensure some reasonable level of safety against a drive failure when one opts for high performance via RAID-0 striping*?
The solution
With four drive bays and performance that maxes-out with three SSDs, the ideal configuration for high performance and built-in backup protection is as follows:
- Triple (or dual) RAID-0 stripe volume (“Master”)— double the SSD speed, double the SSD capacity.
- Single hard drive as a clone backup of Master (“Master.clone”).
Of course, nothing precludes making additional backups to other drives, but the point here is that one internal hard drive maintains a full backup in the same enclosure: a clone backup can be made as often as desired; the backup drive is always there at the ready.
* Separate backups remain essential; theft or calamity pose additional risks beyond failure of a drive.
Example configurations
Possible configurations for high performance use:
- 3 X 120GB SSD = 360GB Master + 500 GB or 750GB or 1TB hard drive.
- 3 X 240GB SSD = 720GB Master + 750GB or 1TB hard drive.
- 3 X 480GB SSD = 1440GB Master + 1.5TB hard drive.
One can certainly substitute two SSDs instead of three or even use a single SSD for starters and go to RAID-0 striping later if needed.
Configuration in Disk Utility
The configuration is shown below: three SSDs and one hard drive.
Clone backups do not require matching capacity to the volume to be cloned, but if one wishes to have a full backup of a full Master volume, then the hard drive must be large enough.
In this example, the largest hard drive available was 500GB, but 1TB models are available with imminent arrival of 1.5TB hard drives as this was written (the Pegasus J4 required 2.5-inch drives no thicker than the 9.5mm standard).
