IBM N Series Hardware Manual page 194

Disk Type
SATA
(or NL-SAS)
Effect of the aggregate
When the disks are added to an aggregate, they are automatically assigned to RAID groups.
Although this process can be tuned manually, there is no separate step to create RAID
groups within the N series platform.
The aggregate might impose some capacity overhead, depending on the DOT version:
DOT 8.1
– In the latest version on ONTAP, the default aggregate snapshot reserve is 0%
– Do not change this setting unless you are using a MetroCluster or SyncMirror
configuration. In those cases, change it to 5%
DOT 7.x
– In earlier versions on ONTAP, the aggregate had a default aggregate snapshot reserve
of 5%. However, the modern administration tools (such as NSM) use a default of 0%
– The default was typically only used in a MetroCluster or SyncMirror configuration. In all
other cases, it can safely be changed to 0%
Effect of the WAFL file system
Another factor that affects capacity is imposed by the file system. The Write Anywhere File
Layou
t (
many file systems, but the effect still exists. Generally, WAFL has a memory usage equal to
10% of the formatted capacity of a drive. This memory is used to provide consistent
performance as the file system fills up. The reserved space increases the probability of the
system locating contiguous blocks on disk.
174
IBM System Storage N series Hardware Guide
Capacity
(decimal GB)
500
750
1000
2000
3000
WAFL) file system used by the IBM System Storage N series has less effect than
Capacity GB Checksum
(binary GB) Type
465 8/9 512 Block
(approximately
698
11.1%)
931
1862
2794
Right-sized Cap.
(binary GB)
413
620
827
1655
2483