The R640 10-Bay + RFB is the refurbished 1U Dell PowerEdge configuration we reach for when a customer needs more than ten drive bays in a single 1U chassis. The Rear Flex Bay (RFB) adds two 2.5" hot-swap drive slots at the rear of the chassis, bringing total drive count to twelve in the same 1U footprint. Pair that with the optional NVMe-capable front backplane and this becomes the most storage-flexible R640 variant: front bays for primary storage, rear bays for boot media, cache tier, or backup target.

The architectural tradeoff matters. The RFB physically occupies space at the rear of the chassis and constrains the secondary riser configuration, which reduces full-height PCIe slot availability. If you do not need the additional rear drives and you want full PCIe slot flexibility for dual NICs plus HBA plus GPU builds, the simpler 10-Bay Standard chassis is the right call. The two extra rear drives come at the cost of one to two PCIe slot positions.

To configure a build, call 1-800-778-1545 or use the quote form below. Every refurbished unit ships under our 180-day warranty with 12+ hour burn-in testing, and volume pricing starts at 5 units.

When 10-Bay + RFB Is the Right Choice

The + RFB chassis earns its place when one of these design patterns applies: you need a dedicated boot drive pair at the rear that does not consume a front bay, you want a separate SSD cache tier physically separated from the primary storage pool, or you have a workload that genuinely needs more than ten drives in a single 1U and a 2U chassis is not an option for rack-density reasons. vSAN ReadyNode builds that want a 12-drive disk group geometry in 1U are another common pattern; the two rear bays carry the cache tier and the ten front bays carry the capacity tier.

If your workload runs fine on ten front bays and you want PCIe flexibility, the 10-Bay Standard chassis is the simpler architecture. If your storage architecture is NVMe-first across all front bays, the 10-Bay NVMe chassis is the right call. The + RFB is specifically for the case where rear drive bays are a hard requirement.

Storage - 10 Front Bays + 2 Rear (RFB)

Ten 2.5" hot-swap front bays on a SAS/SATA backplane (NVMe-capable backplane optional; confirm at quote time) plus two additional 2.5" hot-swap drive bays at the rear of the chassis via the Rear Flex Bay assembly. Total: twelve hot-swap 2.5" bays in 1U.

Common configurations:

• Front bays for data plus rear bays for boot: Ten front bays available for the primary data pool (SAS SSD, mixed SAS/SATA, or all-flash), with the two rear bays running a mirrored OS boot pair. Cleanest separation of boot from data and keeps every front bay available for production storage.
• Front bays for primary plus rear bays for cache: Production data on the front backplane with two SSDs in the rear bays acting as a write-through or read cache tier. Useful for tiered storage architectures and the cache-tier slot in vSAN OSA disk groups.
• Front bays for cold plus rear bays for hot: Higher-capacity spinning disk or near-line storage on the front bays, with high-endurance SAS SSDs in the rear bays for the active working set.

NVMe note: Front-bay NVMe on this chassis depends on the specific backplane ordered. Not every 10-Bay R640 ships with the NVMe-capable backplane. Confirm at quote time before assuming front NVMe is part of your configuration. For NVMe-first deployments where every front bay is NVMe, the 10-Bay NVMe chassis is the correct chassis, not this one.

BOSS alternative for boot: If you prefer the standard BOSS module and ReadyRails II accessories for boot, you free both rear bays for data use. BOSS does not consume a front bay, a rear bay, or a RAID controller channel. We recommend BOSS as the default boot solution on most builds; rear-bay boot is the right call when the customer specifically wants front-accessible boot drives for serviceability or when both rear bays are needed for the cache-tier role and BOSS would conflict with that design.

Storage Controllers at 12-Bay Scale

The 12-bay configuration (10 front plus 2 rear) brings the RAID controller decision into sharper focus than the standard 10-bay. Two key considerations: the rear bays attach via a separate cable harness to the same controller as the front backplane, and write-cache sizing matters more on a 12-drive array than on a 10-drive one.

• PERC H740P (8 GB NV cache, battery-backed): The default recommendation on this chassis. The 8 GB non-volatile cache is the right size for a 12-drive array, and the battery backup is essential for any production data workload.
• PERC H730P (2 GB cache, battery-backed): Acceptable for read-heavy or modest write workloads on this chassis, but the 2 GB cache is on the small side for 12 drives if write throughput matters. Quote H740P unless cost is the constraint.
• PERC H730 (1 GB cache, battery-backed): The 13th-gen-era controller that Dell maintained Mini-PERC slot compatibility for on 14th gen. It works on this chassis and appears frequently on refurbished R640 units as a carryover from prior deployments. Viable but generally a downgrade vs the H730P or H740P on Cascade Lake workloads, and the 1 GB cache is undersized for write activity across 12 drives. Quote it when budget is the driving constraint; otherwise step up.
• PERC H330 (no cache): Light-workload hardware RAID. Not recommended on a 12-drive array carrying production data.
• HBA330 (pass-through): For software-defined storage where vSAN, Storage Spaces Direct, or Ceph manages redundancy across the 12-drive array. Front and rear bays are presented as raw devices to the software layer.
• S140 (software RAID): Dev/test only. Not a production recommendation, particularly at 12-bay scale.

The single-controller-shared-across-front-and-rear architecture means a controller failure takes out access to all twelve drives simultaneously. This is the same single-point-of-failure profile as the 10-Bay Standard, but the higher drive count makes the controller choice more consequential.

Processors

CPU options: Dual 1st Generation Intel Xeon Scalable (Skylake-SP) or 2nd Generation Intel Xeon Scalable (Cascade Lake-SP), socket LGA 3647 on the Intel C620-series chipset. Skylake and Cascade Lake are drop-in compatible. Up to 28 cores per CPU. The platform vocabulary matches the rest of the R640 family.

Our SKU recommendations on this chassis: Intel Xeon Gold 6230 (20 cores, 125W) for the balanced converged-infrastructure build, which is the most common + RFB workload pattern. For vSAN ReadyNode builds with 12 drives feeding a high-VM-density cluster, Gold 6248 (20 cores, 150W) or Gold 6254 (18 cores, 200W) deliver the per-core headroom that vSAN's data services consume.

Heatsink requirement: Any CPU above 150W TDP requires Dell's high-performance heatsink kit and high-performance fan kit. On this chassis specifically, the RFB drive assembly slightly affects rear-chassis airflow, so we are more conservative about top-bin CPU configurations here than on the Standard 10-Bay. Builds with 165W or higher CPUs plus a GPU plus full 12-drive population should run through Dell's thermal restriction tables at quote time; we work this validation in as part of the build review.

Single-socket warning: A single-CPU + RFB build is supported but cuts the platform in half. With one CPU populated only 12 of the 24 DIMM slots are accessible, half the PCIe lanes are inactive, and the NDC and several PCIe slots route through the second CPU and become unavailable. The 12-drive storage layout already implies a workload that justifies dual-socket; single-socket on this chassis is unusual outside of lab and dev contexts.

Memory

Architecture: 24 DDR4 DIMM slots, 12 per CPU across 6 channels at 2 DIMMs per channel. The 6-channel Purley layout is the defining memory feature.

Supported DIMM types:

• RDIMM: Standard enterprise choice. Up to 64 GB per DIMM, 1.5 TB total at full population.
• LRDIMM: Up to 128 GB per DIMM, 3 TB total. The path past 1.5 TB without Optane.
• Intel Optane Persistent Memory (PMem): Cascade Lake L-series CPUs only. Up to 7.68 TB combined with LRDIMM. The vSAN-with-Optane-cache configurations specifically use PMem in App Direct mode and are a known + RFB workload; we walk through the cache-sizing math at quote time when this is in scope.
• NVDIMM-N: Niche; rarely the right answer in 2026.

Memory speed: DDR4-2933 on Cascade Lake Gold 6200 / 5222 at 1 DPC, DDR4-2666 at full 2 DPC population, DDR4-2666 on all Skylake SKUs. Full 24-DIMM population on the + RFB is common because the workloads that justify a 12-drive 1U (vSAN, dense virtualization, mixed converged) are memory-bandwidth-sensitive. The bandwidth gain from full-channel population is worth the speed step down to 2666.

Mixing rules: Match ranks, capacity, and timing within a channel. We do not quote mixed configurations for production builds; matched-set DIMMs avoid subtle stability issues and simplify later expansion.

Networking and PCIe Expansion

Network Daughter Card (NDC): Dell's NDC mezzanine handles primary networking and does not consume any PCIe slot. This matters more on the + RFB than on most R640 variants because the RFB constrains the rear riser. NDC options:

• 4x 1 GbE: Entry-tier, not recommended for the converged workloads that typically justify a 12-drive chassis.
• 2x 10 GbE SFP+ + 2x 1 GbE: Baseline for most + RFB builds carrying enterprise virtualization workloads.
• 4x 10 GbE SFP+: The right call for vSAN clusters and converged builds where storage traffic and application traffic need separation across links.
• 2x 25 GbE SFP28: Strongly recommended for 12-drive all-flash builds and vSAN all-flash nodes. 10 GbE can become the bottleneck on a 12-drive SAS SSD array under load.

PCIe expansion - this is where the RFB tradeoff lives: The Rear Flex Bay assembly physically occupies space at the rear of the chassis and constrains the secondary riser. Riser 2 options that deliver a full-height PCIe slot on the Standard 10-Bay chassis are reduced or eliminated on the + RFB depending on the specific RFB SKU. Practical impact: expect 2 PCIe slots, not 3, on most + RFB builds. Confirm exact riser availability at quote time against your specific chassis revision.

Builds requiring three full-height PCIe cards (typical pattern: dual 25 GbE NIC plus external SAS HBA plus GPU) are not a clean fit on this chassis. The 10-Bay Standard is the right answer for that PCIe budget.

GPU Support

The 1U thermal envelope plus the RFB's rear-airflow impact means GPU support on this chassis is more constrained than on the Standard 10-Bay. Single-width low-profile cards (NVIDIA T4 class) are workable for inference workloads where a single GPU plus a 12-drive storage tier is the architecture. Multi-GPU configurations on the + RFB are not something we quote often; the riser constraint and the airflow impact stack up against this combination, and at that point the Dell PowerEdge R740 16-Bay 2.5" 2U is the better answer.

FPGA single-card builds are supported and behave similarly to single-GPU configurations on this chassis. For any GPU configuration on the + RFB, we validate against Dell's thermal restriction tables at quote time.

Management - iDRAC9 Generation

iDRAC9 Enterprise: Required for production deployment. Remote KVM, virtual media, predictive analytics, Group Manager, Quick Sync 2, Silicon Root of Trust. The 12-drive workload pattern usually means the chassis is unattended at the rack, which makes iDRAC9 Enterprise functionally non-negotiable.

Security baseline: Silicon Root of Trust anchors firmware verification in immutable silicon. System Lockdown mode prevents unauthorized firmware changes after deployment. TPM 2.0 module supported and recommended for any deployment subject to NIST 800-171, CMMC, FedRAMP, HIPAA, or PCI DSS compliance frameworks.

Lifecycle Controller and OpenManage Enterprise: Same Dell management plane as the rest of the R640 family. Lifecycle Controller for per-chassis firmware orchestration; OpenManage Enterprise for fleet-scale firmware compliance, configuration drift detection, and warranty status tracking. Worth integrating on any fleet of more than 20 units.

Power and Cooling

The 12-drive RFB configuration adds two drives to the power and thermal budget vs the standard 10-bay. We size PSUs against the actual build, not against the chassis maximum. As a guideline:

• Light (Silver CPUs, partial RAM, mixed HDD plus SSD): 2x 495W Platinum, peak draw approximately 310W (slightly higher than the Standard chassis due to two extra drives)
• Balanced (Gold 6230, full RAM, all-SAS SSD across 12 bays): 2x 750W Platinum, peak draw approximately 510W
• Heavy (Gold 6248, full RAM, all-SSD 12-bay plus GPU): 2x 1100W Platinum, peak draw approximately 740W

Thermal: Eight hot-plug redundant fans standard. The rear drive assembly does affect rear-chassis airflow slightly. For builds with top-bin 165W+ CPUs plus a GPU, the high-performance fan kit is strongly recommended on this chassis specifically, more so than on the Standard 10-Bay. ASHRAE A3 (40C) ambient support is achievable with the high-performance fan kit, but the operating margin is tighter than on the Standard chassis; we are conservative about A3 sign-off on high-TDP + RFB builds.

Physical Specs & Platform Notes

• Form factor: 1U rack server. 42.8mm H x 434mm W. The RFB assembly extends chassis depth slightly vs the Standard 10-Bay; expect 760-790mm rear-to-front including the RFB rather than the Standard's 735-760mm. Confirm rail kit clearance in shallow racks before order.
• PCIe expansion: Up to 2 PCIe Gen3 slots on most + RFB SKUs (down from 3 on the Standard 10-Bay). Riser 2 options are reduced by the RFB assembly. Builds requiring 3+ full-height cards do not fit cleanly on this chassis.
• Parts availability: Strong. The RFB assembly itself is less common in the secondary market than the standard 10-Bay backplane, but Dell parts coverage remains active and refurbished + RFB units are readily available. PERC controllers, NDC cards, fan modules, and PSUs are the same as the rest of the R640 family.
• Accessories we recommend: Dell LCD bezel (P/N 521RX security bezel, 7M3F1 LCD bezel without security, 9NN24 with security - confirm part at quote time), Dell ReadyRails II sliding rail kit, and the Dell cable management arm (CMA). The CMA matters more on this chassis than most because the rear-bay assembly requires the chassis to be pulled forward for any rear-drive service event.
• Platform notes: Rear drives are accessed by pulling the chassis forward; they are hot-swap but not as fast to service as the front bays. The single PERC managing both front and rear arrays means controller failure isolates all twelve drives. NDC swap and CPU replacement still require powered-down access. BIOS NVMe bifurcation settings must be configured correctly if NVMe expansion cards are added.

Our Assessment

Where it excels: 12-drive vSAN ReadyNodes where the disk group geometry calls for a cache-tier separation between front and rear bays. Converged-infrastructure hosts that benefit from rear-mounted mirrored boot drives keeping the OS off the data pool. Tiered storage builds with a hot working set on the rear bays and capacity on the front. Workloads that legitimately need 12 hot-swap drives in a 1U where rack density rules out the 2U R740xd.

Where to look instead: If you do not need rear bays, the 10-Bay Standard chassis gives you the full PCIe slot budget intact. If your storage is NVMe-first across all bays, the 10-Bay NVMe is the cleaner architecture. If your build requires three or more full-height PCIe slots, the RFB's riser constraint is the wrong tradeoff and the Standard chassis is the right call. If you need more than 12 total drives or any LFF capacity, the Dell PowerEdge R740xd 12-Bay 3.5" 2U platform is the next step up.

Bottom line: The + RFB is a precision pick. It delivers a specific design point - 12 drives in 1U with the rear-bay separation that some workloads genuinely need - in exchange for a measurable reduction in PCIe slot availability. When the workload calls for the rear bays, this chassis is excellent. When it does not, the Standard 10-Bay is the simpler and more flexible build. We ask the workload question first and pick the chassis from the answer.

Where the R640 Fits in 2026

The R640 family is 2 to 3 generations behind current Dell production (R650 / R660). The 10-Bay Standard page covers the generational ladder and the support status in full. + RFB specifically: the rear-bay design point carried forward into the R650 and R660 generations with similar architecture, so the migration path is straightforward when the workload eventually justifies the platform refresh. For 2026 procurement, the + RFB earns its place when 14th gen fleet standardization, budget, or vendor certification keeps the workload on R640 hardware.

Honest Limitations

• RFB constrains PCIe slot availability. The Rear Flex Bay physically occupies riser space, reducing full-height PCIe slot count vs the Standard 10-Bay. Builds requiring 3+ full-height PCIe cards should look at the Standard chassis instead.
• NVMe backplane is not universal on the 10-bay front. Front NVMe support requires the correct backplane SKU. Confirm at quote time. For NVMe-first storage, the 10-Bay NVMe chassis is the correct configuration.
• 2 rear bays, not 4. If you need more than 2 rear drives or want all-rear NVMe, the R640 chassis cannot deliver. The R740xd 2U platform is the next step up for high rear-bay counts.
• Rear bays share the controller with the front backplane. All twelve drives present to a single PERC or HBA. Separate RAID groups can be created across the front and rear bays, but the controller is shared and is a single point of failure for the whole array.
• Rear-bay service requires chassis pull-forward. The rear bays are hot-swap but service is slower than front-bay swap because the chassis must be pulled forward on its rails to access them. The CMA helps; bring it on every + RFB build.
• Tighter thermal margin on top-bin builds. The RFB assembly affects rear airflow. High-TDP CPUs plus GPU on this chassis run closer to the thermal envelope than equivalent builds on the Standard 10-Bay.
• Full R640 family limitations apply. PCIe Gen3, 14th gen platform, 1U thermal envelope. See the R640 10-Bay Standard page for the full Honest Limitations list including the generational positioning vs R650 / R660.

Workload Fit

Where to Look Instead

• Don't need rear bays? The R640 10-Bay 2.5" Standard Chassis is the primary R640 build with the full PCIe slot budget intact.
• NVMe-first storage architecture? The R640 10-Bay 2.5" NVMe replaces SAS/SATA with PCIe-attached NVMe across all front bays.
• Compute-first, fewer drives, wider thermal envelope? The R640 8-Bay 2.5" is the right call when drive count is not the constraint but top-bin CPU thermals are.
• Need 4+ rear drives or higher total drive count in 2U? The Dell PowerEdge R740xd 12-Bay 3.5" is the 2U high-density companion to the R640 1U lineup; up to 24 SFF front bays plus rear bays available.
• vSAN HCI pre-validated? The R640 VxRail E560F is the vSAN-certified version of the 10-bay chassis for VxRail cluster expansion.
• HPE-side equivalent? The HPE ProLiant DL360 Gen10 10-Bay 2.5" is the direct counterpart on the same Intel Purley platform. HPE's rear-bay equivalent is the universal media bay on the DL380 Gen10.
• Step up to 15th gen? The Dell PowerEdge R650 8-Bay 2.5" is the Ice Lake-SP successor with PCIe Gen4 and rear-bay design points that carried forward from the R640.
• Step down to 13th gen for budget? The Dell PowerEdge R630 10-Bay 2.5" is the 13th gen predecessor for budget-constrained refurbished builds.

Ready to Configure?

Tell us your workload, target storage layout across the 10 front and 2 rear bays, NVMe vs SAS/SATA front backplane preference, target memory footprint, NDC choice, and quantity. Our account team returns a fully specced build with formal pricing within 24 hours, including a validated PCIe slot allocation that accounts for the RFB's riser constraint, a confirmed front-backplane SKU, and thermal validation on top-bin CPU configurations. Every refurbished unit ships with the Wholesale Servers 180-day warranty and 12+ hour burn-in testing, and volume pricing starts at 5 units. Call 1-800-778-1545 or use the quote form below.