For the ReadyNAS NV+ (RND4000), is it possible to operate RAID 1 over more than 2 HDDs? If so, how may an additional HDD be designated as the third or fourth mirror of the RAID without resetting and creating the array from scratch?
RAID-1 is a 2-drive array. RAID-1 doesn't make sense with any other number of disks. There are different kinds of RAID used when you have more disks. On a Sparc ReadyNAS (e.g. NV+) you could use RAID-5 (still protects against a single disk failure) or RAID-5. I believe you can add an additional drive as a hot-spare which would automatically be used to rebuild the array after a disk fails.
On Sparc ReadyNAS (e.g. NV+) only X-RAID arrays can have additional drives added into an existing array. See X-RAID in Action. You cannot add a disk as a hot-spare to an X-RAID array, only to Flex-RAID (e.g. RAID-1, RAID-5).
I take it from your response that RAID 1 over more than 2 HDDs is not supported on the RND4000. I appreciate the prompt assistance.
I would like to follow-up on the comments on and learn more about RAID 1. If this topic should now be moved to another forum, please feel free to advise.
RAID-1 is a 2-drive array. RAID-1 doesn't make sense with any other number of disks.
May I ask why not? With a n-HDD RAID 1 array, loss of up to (n-1) HDD is allowable to still permit the array to be online and functional. For example, with a 4-HDD RAID 1 array, a loss of 3 HDDs is allowable. I think in the scenario with a 2-HDD RAID 1 array with a hot spare HDD, while there are 3 HDDs, a loss of only 1 HDD is allowable. That is due to the hot spare not having synchronized live data, being brought online only after the failure of 1 of the other 2, and it taking time for the hot spare to be synchronized.
I don't think I've ever tried Flex-RAID on a Sparc ReadyNAS (I may have a few years ago, but I can't remember). If you want to create a new volume you'll need to delete the existing one and then see what new volume you can create. I think you can only create a two-disk RAID-1 volume, but I could be wrong.
Even if possible it doesn't make much sense to run RAID-1 over more than two disks.
An additional disk can be added as a hot-spare. Your explanation of a hot spare is correct.
4-bay or greater x86 ReadyNAS (e.g. NVX, Ultra, Pro) support Flex-RAID RAID-10 with 4 or more disks installed.
6-bay or greater x86 ReadyNAS support X-RAID2 dual-redundancy (like RAID-6) and Flex-RAID RAID-6.
If you want greater protection than a single disk failure (I do), then I'd strongly recommend you get an x86 ReadyNAS.
You should remember that no matter what RAID configuration you use in the ReadyNAS if the data is stored on one device it is not backed up. For this reason I'd suggest you backup your important data primarily stored on the ReadyNAS regularly e.g. to a USB disk or another NAS device. See Preventing Catastrophic Data Loss
