Several years ago, I upgraded to a 2013 iMac and expanded the storage with a diskless Promise Pegasus 2 four bay external drive enclosure. Until recently, the system had been humming along nicely with two 3 Terabyte and two 4 TB drives, all configured as Pass Thru volumes.
Wanting more storage space for video and photo files, and duplicates on a second volume, I purchased two five TB Toshiba drives when I found them on sale.
I have to admit that the two new drives are not on Promise Technology’s compatibility list.
For the safety of my files, I wanted to set up a RAID 1 configuration on the two larger drives. I set it up using the instructions provided by Promise and everything seemed to be working fine. And then the device began hanging several times a day. The Promise Utility would not open and there seemed to be nothing I could do but pull the power plug.
I don’t know how long the drives worked because I only noticed the failure when I tried to check on the status of my backup files, and could not access the enclosure. I updated the Utility software and the enclosure firmware.
During my research into this issue, I read that many others had experienced similar symptoms, but read no answers. Through experimentation, I found a solution that I wanted to share.
I removed the RAID and made the five TB drives into Pass Thru volumes. I established folders on the drives for those files that I wanted duplicated for redundancy. Many years ago, I purchased ChronoSync from Econ Technologies, www.econtechnologies.com. I set up ChronoSync to automatically synchronize my important files, in the folders, several times a day to prevent their loss if one drive should fail. The utility also tells me if there is a drive or synchronization failure. This system is not as thoughtless as a RAID system, but it seems to work without very much oversight.
An advantage to this method is that I have space on both drives, that is not being duplicated, to use for other purposes.
Since removing the RAID configuration my system has not frozen. I have also noticed that my Pegasus2 seems to sleep when my computer goes to sleep now. I am fairly certain that it had been a long time, if ever, since I had seen the orange power light when the drives were powered up.