I currently have a ReadyNas Duo fitted with 2 x 2Tb drives. I understand the RAID concept that my data is stored on one of the drives which in turn is mirrored on the other drive.
I am contemplating the purchase of a ReadyNas ULTRA 6 PLUS fitted with 6 x 2Tb drives. This will give me 10Tb for data storage which is spread across 5 of the drives, leaving one drive for redundancy. I trust that I have explained that correctly. My confusion is how do I have 10Tb of data backed up on only one 2Tb drive. This is not fully explained in the Netgear tutorial on X-RAID.
I currently have a ReadyNas Duo fitted with 2 x 2Tb drives. I understand the RAID concept that my data is stored on one of the drives which in turn is mirrored on the other drive.
I am contemplating the purchase of a ReadyNas ULTRA 6 PLUS fitted with 6 x 2Tb drives. This will give me 10Tb for data storage which is spread across 5 of the drives, leaving one drive for redundancy. I trust that I have explained that correctly. My confusion is how do I have 10Tb of data backed up on only one 2Tb drive. This is not fully explained in the Netgear tutorial on X-RAID.
Further to horim80's post, the X-RAID and X-RAID2 are based on RAID 5 technology (or RAID 6, if using dual-disk redundancy):
RAID 5 (block-level striping with distributed parity) distributes parity along with the data and requires all drives but one to be present to operate; the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. However, a single drive failure results in reduced performance of the entire array until the failed drive has been replaced and the associated data rebuilt.
RAID 6 (block-level striping with double distributed parity) provides fault tolerance of two drive failures; the array continues to operate with up to two failed drives. This makes larger RAID groups more practical, especially for high-availability systems. This becomes increasingly important as large-capacity drives lengthen the time needed to recover from the failure of a single drive. Single-parity RAID levels are as vulnerable to data loss as a RAID 0 array until the failed drive is replaced and its data rebuilt; the larger the drive, the longer the rebuild takes. Double parity gives time to rebuild the array without the data being at risk if a single additional drive fails before the rebuild is complete.
My confusion is how do I have 10Tb of data backed up on only one 2Tb drive.
You don't.
You have 10tb of data spread across 6 drives.
The spread of the data is handled by the os/raid system, this in turn presents the 10tb of space to use, then it distributes it across the drives as necessary behind the scenes.
One of the reasons for raid is to have more storage than can possibly fit on a single drive.
Thanks guys I think I'm beginning to understand the concept.
If I have an ULTRA 6+ with 6 x 2TB drives, all my data will be spread across all 6 drives. Should one of the drives fail then all my data will still be available, but the system won't run as efficiently until the failed drive is replaced. Is that correct?
Yes. Under the default X-RAID2 settings, the unit can tolerate a single disk failure. Conceptually, 5 disks are for data and 1 disk is for redundancy, however, in reality both data and parity information is striped across all disks.
There is also an option to utilize 2 disks for parity. In this case, 4 disks would be used for data and 2 disks for parity, so you would reduce the overall size of your data volume.
I would use and definately recommend using dual redundancy mode, the extra safety and peace of mind is much more important than the extra space.
in any case, you should understand that no raid system is a substitute for backups, preferably on different davices in different locations. Many factors can cause a raid to fail (software/hardware failure, disk failture, natural disasters, user error/accidental/on-puprose deletion, virus/malware/etc).
