HPE Smart Array Controllers Explained: P408i-a, P816i-a, E208i-a & Legacy P-Series
A plain-English guide to HPE Smart Array RAID controllers — the Gen10 SR-series (E208i-a, P408i-a, P816i-a) versus the Gen8/Gen9 P-series (P420i, P440, P840), what RAID levels each supports, why flash-backed write cache matters, and when to run HBA mode instead of RAID.
TL;DR — which Smart Array do I need?
For an HPE ProLiant Gen10 server, the three SR-series controllers cover almost every case:
- E208i-a — no cache, RAID 0/1/5/10. Great for boot pairs and light RAID, or for HBA/pass-through to software-defined storage.
- P408i-a — 2GB flash-backed write cache, adds RAID 6, 50, 60, and HPE's 1ADM/10ADM three-way mirroring. The default choice for databases and virtualization.
- P816i-a — same feature set as the P408i-a but 16 internal lanes and 4GB cache, for high drive counts (think 24+ SFF bays).
On Gen8/Gen9, the equivalents are the P420i / P440 / P440ar (mainstream RAID) and P840 (high lane count), with the H240 as the HBA option. (Per the HPE Smart Array SR Gen10 Controllers QuickSpecs.)
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What "Smart Array" actually is
Smart Array is HPE's family of internal RAID controllers. They handle the RAID math in hardware, manage the drive cache, and integrate with iLO and Smart Storage Administrator for health and firmware. Two things separate the models: how many drives they can drive (lanes) and whether they have a protected write cache.
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The flash-backed write cache (FBWC) — why it matters
A controller with flash-backed write cache can acknowledge a write the instant it lands in cache, then flush to disk in the background — a large boost for write-heavy workloads like databases. The "flash-backed" part means a small capacitor/flash module preserves that cache through a power loss, so you don't lose in-flight writes.
- E208i-a: no cache — fine for boot/light RAID, not ideal for busy RAID 5/6.
- P408i-a: 2GB FBWC.
- P816i-a: 4GB FBWC + 16 lanes.
If you plan to run RAID 5 or RAID 6 on spinning disks under real load, get a cached controller. The "RAID 5 write penalty" is exactly what the write cache exists to soften.
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RAID levels by controller
| Controller | Cache | RAID levels | Best for |
|---|---|---|---|
| E208i-a | None | 0, 1, 5, 10 | Boot pairs, light RAID, HBA mode |
| P408i-a | 2GB FBWC | 0, 1, 5, 6, 10, 50, 60, 1ADM, 10ADM | Databases, virtualization (mainstream) |
| P816i-a | 4GB FBWC | 0, 1, 5, 6, 10, 50, 60, 1ADM, 10ADM | High drive count / dense storage |
1ADM / 10ADM are HPE's "Advanced Data Mirroring" — three-copy mirrors for maximum read performance and fault tolerance where you can spend the capacity. Supported RAID levels are documented in the HPE Smart Array SR Gen10 Controller User Guide.
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RAID mode vs. HBA mode vs. Mixed mode
SR Gen10 controllers can run three ways:
- RAID mode — classic hardware RAID arrays.
- HBA mode — the controller presents raw drives to the OS. This is what you want for VMware vSAN, Windows Storage Spaces (Direct), ZFS, or Ceph, which prefer to manage disks themselves.
- Mixed mode — some drives in hardware RAID, others exposed raw.
If you're building software-defined storage, don't fight it with hardware RAID — set the controller to HBA mode (or buy the cache-less E208i-a) and let the software layer own the disks.
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Buying notes (the honest version)
- Cache modules and batteries age. On refurbished cached controllers, confirm the FBWC module and its energy pack are healthy — a dead capacitor pack drops the controller to write-through and tanks write performance.
- Firmware matters. Update Smart Array firmware to a current baseline for your ProLiant generation before going to production.
- Controller and backplane must match the chassis generation. A Gen10 P408i-a (modular "a" form) seats differently than a P408i-p (PCIe "p" card). Match the suffix to your server's slot.
Pro Disk Network stocks Smart Array controllers as an independent reseller of genuine HPE hardware (we are not affiliated with HPE); refurbished units are tested before shipping. See HP server storage.
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FAQ
Is the onboard controller enough? For RAID 0/1/5/10 on a handful of drives, often yes. Move up to a P408i-a for RAID 6 or a real write cache.
P408i-a or P816i-a? Lane count. Up to ~8-12 drives, the P408i-a is plenty. For 16-24+ drives, the P816i-a's 16 lanes avoid a bottleneck.
Can I move arrays between controllers? HPE supports array roaming within the same controller family/firmware baseline, but always back up first and read the User Guide for your exact models.
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Next in this series: HP Enterprise SAS Hard Drives decoded and choosing the right RAID level. Overview: HP Storage Solutions guide.
Sources: HPE Smart Array SR Gen10 Controllers QuickSpecs; HPE Smart Array SR Gen10 Controller User Guide.