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Understanding how HDP works with HNAS

Using HDP with HNAS provides many benefits.

HDP with HNAS provides the following benefits:

  • Improves performance by striping I/O across all available disks
  • Supports scalability of larger LUs (typically up to 64 TiB)
  • Reduces the need to use the span-expand command, and eliminates dynamic read balancing (DRB) limitations. When HDP thin provisioning is used, a pool can be expanded in small increments any number of times. However, if you expand a storage pool, make the increments as large as the initial size of the storage pool to avoid performance problems.
  • File system creation or expansion still fails safely, even in the presence of thinly provisioned pools

To fully realize those benefits, see the HDP configuration guidelines in the Hitachi NAS Platform Storage Pool and HDP Best Practices (MK-92HNAS048).

As a general rule, you should make a rough forecast of how much data storage capacity will be needed in the next 12 to 24 months, then configure your DP-Vols to be just a little larger than your estimate. If you overestimated your data storage requirements, not too much space will have been wasted; if you underestimated your data storage requirements, you can always add a second, equally large stripeset using the span-expand command, then continue to expand the DP pool in increments as small as desired.

Some limitations with HDP thin provisioning and HNAS exist. Consider the following:

  • Some storage arrays and systems do not over-commit by more than a factor of ten to one.
  • The amount of memory the storage needs for HDP is proportional to the size of the (large, virtual) DP-Vols, not the (smaller, real) pool volumes. Therefore, massive over-commitment causes the storage to prematurely run out of memory.


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