ULLtraDIMM
SanDisk solid state storage on the DDR3 memory bus.
The ULLtraDIMM is a solid state storage device from SanDisk that connects flash storage directly onto the DDR3 memory bus. Unlike traditional PCIe Flash Storage devices, the ULLtraDIMM is plugged directly into an industry standard RDIMM memory bus slot in a server, providing deterministic (consistent) known latency to enable applications to be streamlined for improved performance.
- Form factor
- JEDEC MO-269 DDR3 RDIMM
- Voltage support
- 1.35 V and 1.5 V
- Ddr3 transfer rates
- 800–1333 MHz (both voltages), 1.5 V @ 1600 MHz
- Ecc usage
- DDR3 ECC bits verify data integrity across memory bus; separate ECC for flash array
Lore & Background
The ULLtraDIMM was designed to place flash storage directly on the DDR3 memory bus, using standard RDIMM slots in servers. This placement allows the CPU to treat the device's ECC in the same manner as ECC from a memory DIMM, with single symbol errors corrected. The DDR3 ECC bits are not stored in the flash array; a separate ECC scheme protects data within the flash. Memory interleaving of standard RAM is not affected by the presence of ULLtraDIMMs. The device supports both 1.35 V and 1.5 V operation across a range of DDR3 transfer rates, and at 1.5 V it can operate at 1600 MHz. UEFI/BIOS updates are required for the system to properly recognize the ULLtraDIMM as a block device and to avoid halting the bootstrap sequence.
Reader's Guide
The ULLtraDIMM's significance lies in its integration of flash storage directly onto the DDR3 memory bus, a departure from traditional PCIe-based flash storage. By plugging into standard RDIMM slots, it offers deterministic latency, which allows applications to be streamlined for improved performance. The device uses DDR3 ECC bits to verify data integrity across the memory bus, with the CPU handling ECC errors as it would for standard memory DIMMs—correcting single symbol errors. If errors are detected, the device driver re-runs the transfer. A separate ECC scheme protects data within the flash array itself. The ULLtraDIMM is compatible with the JEDEC MO-269 DDR3 RDIMM specification and supports both 1.35 V and 1.5 V operation at various DDR3 transfer rates. Its presence does not affect memory interleaving of standard RAM. However, UEFI/BIOS updates are necessary for the system to recognize the device as a block device and to prevent the bootstrap sequence from halting. This design provides a unique approach to reducing storage latency in server environments.
Did You Know?
- DDR3 ECC bits are used to verify data integrity across the memory bus, but a separate ECC scheme protects data in the flash array.
- UEFI/BIOS updates are required to properly recognize the ULLtraDIMM as a block device.
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