Understanding Capacity Differences: Two ReadyNAS Ultra NAS Units in Mirrored Configuration
In a mirrored configuration, two ReadyNAS Ultra Network Attached Storage (NAS) units work together to provide data redundancy and increased reliability. This setup involves one primary NAS unit and a secondary unit, which mirrors the data from the primary unit. In this article, we will discuss the capacity differences that arise in a mirrored configuration and how to interpret the capacity reporting.
Mirrored Configuration: How it Works
In a mirrored configuration, also known as RAID 1, all data written to the primary NAS unit is duplicated to the secondary unit. This means that both units have an identical copy of the data at any given time. In case of a failure in the primary unit, the secondary unit can take over, ensuring data availability and minimizing downtime.
Capacity Reporting in a Mirrored Configuration
When monitoring the capacity of a mirrored configuration, it is essential to understand that the secondary unit's capacity is entirely utilized for mirroring the primary unit's data. Therefore, the secondary unit will show 100% used capacity and 0 available capacity.
For example, if you have two 2 TB ReadyNAS Ultra units in a mirrored configuration, the primary unit will still have 2 TB free, while the secondary unit will show 100% used capacity and 0 available capacity. This is expected behavior and does not indicate a problem with the secondary unit.
Interpreting the Capacity Reporting
To ensure that the capacity reporting is accurate, you can use tools like mdadm, which is a Linux software RAID management utility. The output from mdadm will show the status of the mirrored configuration and the capacity usage of each unit.
# mdadm --detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Thu Aug 18 14:22:44 2022
Raid Level : raid1
Array Size : 1953512832 (1862.89 GiB 2000.28 GB)
Used Dev Size : 1953512832 (1862.89 GiB 2000.28 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Thu Aug 18 14:23:17 2022
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : server:0 (local to host server)
UUID : 3d2a4e3a:8e3c6f7a:8c0f6e12:7a20e10c
Events : 25
Number Major Minor RaidDevice State
0 8 1 0 active sync /dev/sda1
1 8 17 1 active sync /dev/sdb1
In the example above, you can see that both devices (/dev/sda1 and /dev/sdb1) are active and in sync. The Array Size shows the total capacity of the mirrored configuration (1862.89 GiB or 2000.28 GB), while the Used Dev Size indicates the capacity used by each device (also 1862.89 GiB or 2000.28 GB).
- In a mirrored configuration with two ReadyNAS Ultra units, the secondary unit's capacity is entirely utilized for mirroring the primary unit's data.
- The secondary unit will show 100% used capacity and 0 available capacity, while the primary unit still has free capacity.
- To ensure accurate capacity reporting, use tools like
mdadmto monitor the status of the mirrored configuration.