RAID configuration with Promise Pegasus

The array is the set of drives joined together. Inside the Disk Array, you can put one (or more) Logical Drives. The Logical Drives are what the Mac can detect. You are able to set the RAID level (0, 1, 1E, 10, 5, 6) when you create the Logical Drive.

A disk array's maximum size is (the number of drives) multiplied by (the smallest drive). So if you tell the Pegasus to make an array out of 6 drives, 5 of which are 3TB and one of which is 2TB, then the total will be 12TB (6 x 2TB).

If you take a physical drive out and replace it with a larger drive, the Pegasus R will rebuild to the original dimensions of the array* and you will not be able to take advantage of the larger size unless you delete the array and make a new array. Keep in mind the maximum array size will still be limited by the smallest drive in the array.

The best way to increase the drives is to backup your files to a second Pegasus or another storage medium; replace all the drives at once; create a new array over the larger drives; create a new logical drive to take up the new larger array; format that in Disk Utility; then restore your files from backup.

For more information please consult the Wikipedia articles on "RAID" and "Standard RAID Levels". We would be happy to take your questions over the phone as well, at Promise Technical Support, 408-228-1500.

*Arrays containing RAID-0 logical drives cannot be rebuilt onto a blank drive, as they have no redundant data for the other drives to check. For this reason, the loss of any drive in a RAID-0 logical drive will take the logical drive offline.

Joe Engledow, Promise Technical Support, http://support.promise.com

Think of it like matryoshka nesting dolls. Inside the array, there's a logical drive. Inside the logical drive, that's up to your OS to manage the partition. Inside the partition is the formatting, and the catalog, and the files, again all managed by your OS.

Promise Pegasus and Vtrak can stretch the array and the logical drive out to cover larger drives, once all the drives in the array are replaced with new drives and allowed to rebuild before changing the next drive down; that's called Data Migration and is available within the graphic utility or the command line interface, please check your manuals and the Promise Knowledge Base http://kb.promise.com. Migration will take hours, sometimes days, to increase the array and, if you add a check to the Expand Logical Drive check box, the logical drive will expand to fill the larger array. The sticking point is that the MacOS partition inside the logical drive can't stretch to cover the added space.

Please see this earlier Support Communities question for more info.

https://discussions.apple.com/thread/4895990

With ZFS available on the Mac, what we all really need is a simple container that is thunderbolt connected, and the ability to treat its contents as JBOD. I continue to be amazed at Promise not providing the ability to buy such a "box". I don't need "support" for my disk drives. ZFS provides the ability to deal with disk errors in the most resilient mechanisms in the industry. Why must we be burdened with products focused on limited technologies such as what currently exists for conventional raid? ZFS will allow your disk space to increase once all the small disks are gone. Some people need read optimizations and others need write optimizations. ZFS provides the ability to use small, high performance SSDs to optimize writes while still providing power fail survivability due to the transactional nature of the implementation. Data integrity on your disk surfaces is maintained through block validations and user configurable scrubbing which will read and check all block checksums and recover bad data from Raid-Z or Mirrored disks.

At some point, we need to move on past the limitations of Raid implementations of today. ZFS is the solution available right here and right now.

https://openzfsonosx.org