Hi team!
Here's a summary of several FAQs about capacity of LUN.
Question 1
What is the minimum unit for the capacity of a LUN?
Answer
The minimum unit for the capacity of a LUN is one block (512 bytes).
When creating a LUN, you can specify larger units that are MBs, GBs, or TBs in size.
You may enter a value that is accurate to three digits after the decimal point.
However, the value actually sent to the service module is converted to blocks.
Therefore, in some scenarios the capacity of a LUN must be measured in blocks.
For example, a remote replication requires the capacities of the primary and secondary LUNs to be identical.
Question2
Why is the displayed capacity of a LUN inconsistent with the value specified when it is created?
Answer
The capacity of a service module is measured in blocks.
If a LUN is created in DeviceManager with a capacity measured in MBs, GBs, or TBs (accurate to a maximum of three digits after the decimal), the value is rounded down.
After the LUN has been created, the LUN capacity obtained from the service module is also measured in blocks and then converted to a value in the requested unit of measurement, accurate to a maximum of three digits after the decimal point.
For example, 68.078 GB is converted into 73098195894.272 bytes and then 142769913.856 (73098195894.272/512) blocks.
The value that is actually sent to the service module is 142769913.
After a LUN query, the returned number of blocks is also 142769913,
which can be converted into 73098195456 (142769913 x 512) bytes.
To ensure that the capacity is displayed normally, the capacity measured in bytes is further converted into 68.077999591827392578125 GB.
This becomes 68.077 GB because the value only needs to be accurate to three digits after the decimal point.
Therefore, if the capacity entered during LUN creation is not an integral multiple of a block, the displayed capacity of the LUN will be inconsistent with that specified during creation.
Question3
How do I query the exact capacity of a LUN?
Answer
In DeviceManager, select the LUN you want to query, right-click, and choose Properties from the shortcut menu.
Hope this can help you with similar questions.
