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Initial RAID 5 Configuration for Later RAID 6 Expansion
I’m an “aspirant,” not a guru. I just received a ReadyNAS RN628X, which will become the main NAS with my 7-year-old Ultra 6 Plus as backup. After installing 6+ drives of mixed capacity in the 628, I was surprised that the NAS was being configured as XRAID2/RAID 6 instead of RAID5. That meant a much smaller volume capacity than the XRAID2/RAID 5 volume in the U6P with the same drive configuration.
To understand why, I searched the community forum and found this very helpful discussion about XRAID, RAID 5, RAID 6, and NASes </= 6 bays or >6 bays.
It appears that a 6+ bay NAS populated with mixed capacity drives requires more careful configuration when starting from a Factory Default.
Initially, I need at least a volume with at least 16TB usable. In the future, I want to use disks with the following capacities: 8TB, 4TB, 2TB, and 1TB. Currently, I only have 3 drives of each capacity, but I expect to buy additional 8TB drives over time.
Initial Configuration: I am going to restart the 628 with a Factory Default and five of the following drives for an initial RAID 5 volume: 2x8TB, 1x4TB, 1x2TB, and 1x1TB. My understanding is that, in general terms, the volume will have the following RAID 5 layers with single redundancy: 8TB, 4TB, 2TB, and 1TB. Eventually, I plan expand the volume to 6+ drives, which will expand the volume to RAID 6. Am I correct about the following?
A. When a third 8TB drive is added to the initial configuration, the 4TB, 2TB, and 1TB layers of the 6-drive volume will convert to RAID 6, the 8TB layer will remain RAID 5, and the total capacity will increase only by 4TB.
B. After step A above, a fourth 8TB drive is added. This should convert the 8TB layer to RAID 6 and give the entire volume dual redundancy.
C. If in step B above the fourth 8TB drive is swapped with the single 4TB instead of added, then the result is the same as B except the total capacity will increase only 4TB, the difference between the 8TB added and the 4TB removed.
D. If after C above, the 4TB drive is added without removing any drives, then the total capacity is increased by 4TB because the 4TB is added to an existing 4TB layer.
E. If the 4TB drive is omitted from the Initial Configuration above, then the later addition of a 4TB drive to a 4x8TB, 1x2TB, and 1x1TB volume will increase total capacity only by 2TB because there are only 8TB, 2TB, and 1TB layers in RAID 6.
In a 6+ NAS, it appears a RAID 5 configuration of 2x8TB, 1x4TB, 1x2TB, and 1x1TB drives will allow the most efficient and flexible use of those drive capacities in RAID 6 expansion.
Aborted the attempt to answer my own questions:
3 Replies
Replies have been turned off for this discussion
coloatty wrote:
Initially, I need at least a volume with at least 16TB usable. In the future, I want to use disks with the following capacities: 8TB, 4TB, 2TB, and 1TB. Currently, I only have 3 drives of each capacity, but I expect to buy additional 8TB drives over time.Initial Configuration: I am going to restart the 628 with a Factory Default and five of the following drives for an initial RAID 5 volume: 2x8TB, 1x4TB, 1x2TB, and 1x1TB. My understanding is that, in general terms, the volume will have the following RAID 5 layers with single redundancy: 8TB, 4TB, 2TB, and 1TB.
I realize that the Initial Configuration adds up 15TB of usable capacity, but that instead of 16TB will be enough to start.
Aborted the attempt to answer my own questions:
Re: A. above.
With six disks, the only array to reshape automatically to raid6 was md127–/dev/md/data-0. There was enough drive quantity/capacity for other arrays to reshape as raid6, but they did not do it automatically prior to the abort.
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