The most common reason for the HA deployement to fail is disk access latency within Ontap select.
One of the requirements on hardware level is a supported raid controller and write-back enabled.
https://www.netapp.com/us/media/tr-4517.pdf - Product Architecture and Best Practices
page 8, 9 and 19
RAID Controller Configuration for Local Attached Storage
All locally attached disks that provide ONTAP Select with backing storage must sit behind a RAID
controller. Most commodity servers come with multiple RAID controller options across multiple price
points, and each with varying levels of functionality. The intent is to support as many of these options as
possible, providing they meet certain minimum requirements placed on the controller.
The RAID controller that is managing the ONTAP Select disks must meet the following requirements:
• The hardware RAID controller must have a battery backup unit (BBU) or flash-backed write cache
(FBWC) and support 12Gbps of throughput.
• The RAID controller must support a mode that can withstand at least one or two disk failures (RAID 5,
RAID 6).
• The drive cache should be set to disabled.
• The write policy should be configured for writeback mode with a fallback to write through upon BBU or
flash failure.
• The I/O policy for reads must be set to cached.
All locally attached disks that provide ONTAP Select with backing storage must be placed into RAID
groups running RAID 5 or RAID 6. For SAS drives and SSDs, using RAID groups of up to 24 drives
allows ONTAP to reap the benefits of spreading incoming read requests across a higher number of disks,
providing a significant gain in performance. With SAS/SSD configurations, performance testing was done
against single-LUN versus multi-LUN configurations. No significant differences were found, so for
simplicity’s sake, NetApp recommends creating the fewest number of LUNs necessary to support your
configuration needs.
