Previous Limitations
Prior to the release of ONTAP 8, individual aggregate sizes were limited to a maximum of 2TB for FAS250 models and 16TB for all other models.
The limitation on aggregate size, coupled with increasing density of disk drives, served to limit the performance of the overall system. NetApp, like most storage vendors, increases overall system performance by parallelizing disk writes to many different spindles (disk drives). Large capacity drives, therefore limit the number of spindles that can be added to a single aggregate, and therefore limit the aggregate performance.
Each aggregate also incurs a storage capacity overhead of approximately 7-11%, depending on the disk type. On systems with many aggregates this can result in lost storage capacity.
However, the overhead comes about due to additional block-checksumming on the disk level as well as usual file system overhead, similar to the overhead in file systems like NTFS or EXT3. Block checksumming helps to insure that data errors at the disk drive level do not result in data loss.
Data ONTAP 8.0 supports a new 64bit aggregate format, which increases the size limit to approximately 100TB (depending on storage platform) thus restoring the ability to configure large spindle counts to increase performance and storage efficiency.
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