2015-07-14 03:01 AM
I need some help with interpreting how aggregate's total space is calculated and presented, as I need to conduct my own calculations for a purpose of future scale-up of one of our arrays.
Suppose I have an aggregate consisting of 43 SAS 600 GB disks. System Manager shows that each of those disks has 546,88 GB of usable size. The aggregate has 3 raid groups (rg size = 15), which means there are 6 parity disks. That leaves me with 37 data disks. This number multiplied by the disk usable size equals about 19,76 TB, yet the system shows that the aggregate's total space is 17,78 TB. Aggregate metadata occupies 739.5MB according to output of the aggr show-space command.
So where does the difference of nearly 2 TB come from?
2015-08-05 02:22 AM
WAFL reserves approximately 10% of space in the aggregate for aggregate level metadata, and for performance reasons. A part of the remaining 90% of space is also reserved for aggregate Snapshot copies. The percentage of space reserved for aggregate Snapshot copies can be controlled by snap reserve -A. The default value is 5%. That is 5% of 90% of space, i.e. 4.5% of total space in the aggregate. The remaining space can be used for flexible volumes in the aggregate.
The distribution of space in traditional volumes is similar. WAFL reserves approximately 10% of space for performance reasons, and for some part of the metadata. A part of the remaining 90% of space is reserved for Snapshot copies. The percentage of space that is reserved for Snapshot copies can be controlled by snap reserve. The default value is 20% and that is 20% of 90% of space, i.e. 18% of the total space in the aggregate. The remaining space can be used for the active file system, except when Snapshot copies exceed their reserve, thus spilling into the active file system space.
See KB 3011274 for more Information.
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2015-08-05 04:16 AM
Try below command which will give you readable output
> aggr show_space -g <aggregate_name>
In that you will see the total space : which is addition of the Data Disk in the Aggregate.
WAFL reserve: which is 10% for metadata and other stuffs.
Aggr Snap Reserve: which depends on the % you reserved
Rest of the space is Usable spacewhich can be used to create volumes.