#NetApp announced compaction as an extra form of data reduction in ONTAP v9.0. What is it?
Compaction applies to NetApp’s all-flash FAS arrays. A blog post by Adam Bergh, data centre practise lead at Presidio, explains that multiple IOs can be written more efficiently, from a WAFL space point of view, if they are stored in a 4KB block.
This block size is the one WAFL (ONTAP’s Write Anywhere File Layout) uses when it writes to disk. Avoiding unused space in such 4KB blocks is a good idea.
The aggregation of multiple IOs into a 4GB block takes place with 4KB logical blocks as they are being organised before being written to disk.
Each IO is put in a 4KB logical block, even if it is less than 4KB in size. With compaction, multiple IOs are added to a 4KB logical block until it is full and then a fresh logical block is used for the next IOs.
Compaction works separately from deduplication and compression and so is additive to them.
http://www.theregister.co.uk/2016/06/13/netapps_4kb_block_writes_can_hold_more_data/
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