When an AS400/IBM i storage conversation turns to IBM FlashSystem, the real decision usually is not just "how much capacity," it is whether external SAN-attached storage belongs in this year's upgrade budget at all, and if so, which FlashCore Module generation the quote should actually specify.

Internal DASD vs. external FlashSystem: the first decision

Internal DASD stays the simpler and often cheaper path for organizations whose storage growth and performance needs are stable. IBM FlashSystem becomes worth evaluating once one of three things happens: internal capacity is running out, internal I/O performance is limiting the workload, or the business wants to consolidate IBM i storage onto shared infrastructure serving other platforms. If none of those apply yet, a FlashSystem line item in this year's upgrade budget is probably premature.

FlashCore Module generations: what actually changes

IBM has released four FlashCore Module generations (FCM1 through FCM4), each cataloged across a 4.8 TB to 38.4 TB usable capacity range. For a buyer, the generation question is rarely a free choice. It is set by what the target FlashSystem array model supports and what the current IBM configurator is quoting:

  • FCM1 and FCM2 are legacy generations, relevant mainly as exact-match replacement or expansion for an already-installed array of that generation.
  • FCM3 remains common on arrays purchased in the recent past, before FCM4 became the default quote.
  • FCM4 is IBM's newest generation and is typically what a new FlashSystem purchase is quoted with today.

The part number and feature code both need to match the exact array model and configuration, since the same capacity within a generation can carry more than one valid part number.

Sizing the upgrade against real usage, not a spec sheet

Before requesting a FlashSystem or FlashCore Module quote, pull current DASD busy percentage and I/O wait trends from the existing environment. A capacity shortfall and a performance shortfall call for different sizing conversations, and vendors will size very different configurations depending on which problem is actually being solved.

Budgeting the full project, not just the drives

A FlashCore Module line item is only part of the cost. A realistic FlashSystem upgrade budget also accounts for the Fibre Channel host adapter on the Power side if one is not already installed, SAN fabric or zoning work, migration and cutover planning, and staff time to validate the new storage path before cutting workloads over. Treating the drives as the whole project is one of the most common ways a FlashSystem budget runs short.

FAQ

Do I need to replace my internal DASD to add FlashSystem storage?

No. IBM FlashSystem storage attaches externally over SAN and does not require replacing internal DASD. Many organizations run FlashSystem alongside existing internal storage, using it for growth capacity or workloads that benefit from external, shareable storage.

Should I order FCM3 or FCM4 for a new FlashSystem purchase?

FCM4 is IBM's newest generation and is typically what gets quoted on a new FlashSystem order today. FCM3 remains common on arrays purchased more recently but before FCM4 became the standard quote. The right choice usually follows what your FlashSystem array model and quote already specify rather than a free choice between the two.

What triggers a FlashCore Module upgrade project?

The most common triggers are internal DASD running out of capacity or performance headroom, a broader Power hardware refresh where storage is being reviewed as part of the same budget, or a decision to consolidate IBM i storage onto shared external infrastructure with other platforms.

Does upgrading FlashCore Module generation require a full array replacement?

Not necessarily. Adding capacity within a compatible generation can sometimes be done as an expansion. Moving to a newer FlashCore Module generation may require confirming the array's controller and firmware support that generation, which can mean an array-level upgrade rather than a simple drive swap.

Related reading

Planning a storage refresh alongside a Power upgrade?

If FlashSystem storage is coming up as part of a broader AS400 or IBM i modernization project, size the storage decision and the server decision together rather than as two separate purchases.