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"Flexible Smart Array" is HPE's name for the modular RAID controllers that mount in a dedicated slot instead of consuming PCIe — a design from the ProLiant Gen8/Gen9 era that still runs in thousands of servers today. Here's what the term actually means, what these controllers can (and can't) connect, and how the idea evolved into today's SR and MR controllers.
Last updated: 2026
If you've worked on a ProLiant Gen8 or Gen9 server, you've almost certainly handled a Flexible Smart Array controller — models like the P440ar or P840ar, identifiable by the "ar" suffix. The defining trait is right there in the name: instead of occupying a PCIe expansion slot like a plug-in RAID card, a Flexible Smart Array controller mounts on a dedicated connector on the system board, leaving every PCIe slot free for network adapters, GPUs, or additional storage cards. That single design decision is why the concept never really went away — it just changed names as the generations advanced.
What "flexible" actually means
HPE's Gen8 and Gen9 Smart Array lineup came in two physical styles: standalone PCIe cards (P440, P840) and their "-ar" siblings (P440ar, P840ar, plus the H240ar Smart HBA) built for the dedicated system-board slot. Electrically they deliver the same Smart Array feature set — hardware RAID across levels like 0, 1, 5, 6, 10, 50, and 60, flash-backed write cache (FBWC), and management through Smart Storage Administrator — but the modular version preserves your expansion slots. On Gen9 servers, cache protection moved to the shared HPE Smart Storage Battery, a single battery on the system board that can back the write cache of multiple controllers at once, replacing the per-controller batteries of earlier generations.
What they connect — and a correction to the original post
An earlier version of this article claimed Flexible Smart Array controllers manage NVMe drives. That was wrong, and worth correcting plainly: Gen8/Gen9 Flexible Smart Array controllers support SAS and SATA devices — hard drives and SSDs — over 6 and 12 Gb/s links. NVMe drives in servers of that era connected directly to PCIe lanes, bypassing the RAID controller entirely. RAID controllers that natively handle NVMe alongside SAS and SATA ("tri-mode") only arrived with the SR and MR controller families in later generations. If you're weighing NVMe for an HPE server, our guide to NVMe drives in HPE servers covers how that connectivity works.
How the idea evolved: Gen10's "-a" and today's SR/MR controllers
ProLiant Gen10 kept the concept and changed the suffix: modular controllers like the E208i-a, P408i-a, and P816i-a (the "-a" for the dedicated modular slot) took over from the "-ar" family, still SAS/SATA, still slot-free.
From Gen10 Plus onward, HPE split the portfolio into two families that continue today. SR controllers carry the Smart Array lineage forward, while MR controllers are built on Broadcom MegaRAID technology — and both bring the change the older controllers never had: tri-mode operation, connecting NVMe, SAS, and SATA drives through the same controller. The spirit of "flexible" lives on in the "-o" suffix: controllers like the MR416i-o Gen11 mount in the server's OCP 3.0 slot rather than a PCIe slot — the modern equivalent of the old dedicated connector — while "-p" models remain conventional PCIe cards. Current Gen11 MR controllers add hardware security measures as well, including SPDM certificate-based authentication with iLO 6.
| Era | Slot-free designation | Example models | Drive support |
|---|---|---|---|
| Gen8 / Gen9 | "-ar" (Flexible Smart Array) | P440ar, P840ar, H240ar | SAS / SATA |
| Gen10 | "-a" (modular) | E208i-a, P408i-a, P816i-a | SAS / SATA |
| Gen10 Plus – Gen12 | "-o" (OCP 3.0 slot) | MR416i-o, MR408i-o, SR-series | Tri-mode: NVMe / SAS / SATA |
Maintaining Gen9 or Gen10 servers today
Plenty of production Gen9 and Gen10 systems will run for years yet, and their controllers have two practical realities. First, replacements must match: a "-ar" or "-a" controller only fits its dedicated slot and its server generation, so replace like with like — the fastest way to find the right genuine part is to shop by your exact machine on our HPE parts by server model pages. Second, cache protection is a wear item: the Smart Storage Battery or capacitor backing your FBWC degrades over time, and iLO will flag it when it does. Keeping a replacement Smart Array controller battery on hand is cheap insurance for any server whose write cache matters.
Frequently asked questions
What is an HPE Flexible Smart Array controller?
A modular Smart Array RAID controller from the ProLiant Gen8 and Gen9 era that mounts on a dedicated system-board connector instead of occupying a PCIe expansion slot. Models carry an "ar" suffix, such as the P440ar and P840ar, and deliver the same hardware RAID features as their PCIe-card siblings while leaving expansion slots free.
What does the "ar" suffix mean on HPE controllers?
It identifies the flexible, modular version of a controller, designed for the dedicated slot on Gen8 and Gen9 system boards. The equivalent designation became "-a" on Gen10 modular controllers and "-o" on current-generation controllers that mount in the OCP 3.0 slot.
Do Flexible Smart Array controllers support NVMe drives?
No. Gen8 and Gen9 Flexible Smart Array controllers support SAS and SATA hard drives and SSDs. NVMe drives in that era connected directly to PCIe lanes rather than through the RAID controller. Controllers that natively manage NVMe alongside SAS and SATA arrived later with the tri-mode SR and MR families.
What replaced Flexible Smart Array controllers?
Gen10 continued the modular concept with "-a" controllers like the P408i-a. From Gen10 Plus onward, HPE's portfolio split into SR controllers, continuing the Smart Array lineage, and MR controllers based on Broadcom MegaRAID technology, with "-o" models mounting in the OCP 3.0 slot to preserve PCIe slots the same way the old flexible controllers did.
What is the difference between HPE SR and MR controllers?
Both are current HPE storage controller families with tri-mode NVMe, SAS, and SATA support. SR controllers continue the Smart Array heritage, while MR controllers are built on Broadcom MegaRAID technology and are managed with MegaRAID-family tools. Volumes are not portable between the two families, so servers standardize on one or the other.
Do Smart Array controllers need a battery?
Controllers with flash-backed write cache rely on a battery or capacitor to protect cached data during power loss. On Gen9 servers this is the shared HPE Smart Storage Battery, which can back multiple controllers at once. These energy packs are wear items, and iLO reports when one needs replacement.
The bottom line
Flexible Smart Array controllers solved a real problem — full hardware RAID without sacrificing a PCIe slot — and the solution proved durable enough that every generation since has kept a slot-free option, from Gen10's "-a" modular controllers to today's OCP-mounted "-o" SR and MR models with tri-mode NVMe support. If you're keeping a Gen9 or Gen10 fleet healthy, match replacements to your exact server on our HPE parts by server model pages, keep an eye on your cache batteries, and if you're not sure which controller your server takes, contact our team — we'll confirm the right genuine HPE part before you order.
