Expanding file systems on flash storage

Storage Subsystem Administration Guide for Hitachi NAS Platform

Part Number

If an untiered span (or a single tier of a tiered span) has stripesets on two or more compressed HDP pools, the server cannot determine which stripeset, and, therefore, which HDP pool can most safely supply space for a filesystem-expansion.

In this scenario, file systems cannot be auto-expanded. If all compressed stripesets are on the same HDP pool, or if two compressed stripesets are in different tiers, this condition does not apply, and auto-expansion works normally.

To help identify spans with multiple compressed pools, the sd-list command's Con column, which displays information about filesystem auto-expansion, displays an MCP symbol (Multiple Compressed Pools).

For example:

sd-list command

If an untiered span (or one tier of a tiered span) resides on two or more compressed HDP pools, filesystem auto-expansion will be disabled on that span, because the server cannot determine which HDP pool can most safely provide new space. The span-expand command will not place a span into this state without an override. If you try to add a second HDP pool to a span or a tier, span-expand requires you to supply the --permanently-disable-filesystem-auto-expansion switch to show that you understand the consequences. This switch is not accepted in any other circumstances.

Using manual file system expansion

During manual expansion of a span that resides on multiple compressed HDP pools, you must explicitly specify a stripeset by running the following CLI command:

filesystem-expand --on-stripeset

Alternatively, in NAS Manager, the Expand File System page shows a list of stripesets from which you can select if the server cannot choose: