Tech Brief
NANDrive™ Power Interrupt Data Protection
The Problem		The loss of data during a power fail event has been aconcern for many memory technologies, particularly
during program operations. Planar (2D) NAND flash
memories, for example, have been vulnerable to “pairedpage” data corruption issues.
NAND flash is written in pages and a failed write to one
page could lead to corruption of the data in its pairedpage. MLC NAND stores its two bits of data in one
memory cell.
These two bits are in two different paired pages,
which are programmed in separate stages because
programming is done one page at a time. This meansthat if the power fails while writing to one page, the datain the paired page can also get corrupted. This typeof error is difficult for a higher level file system (NTFS,XFS, Ext4, etc.) to handle because the host file system
may have transaction failsafes in place, but it would
have no idea that the paired page was affected. The
data in the paired page may belong to a completelydifferent file.
If this was a DLL or runtime file it could lead to a nonfunctional operating system or application on thedrive. The contents of the paired page will containuncorrectable (UNC) data where the charge state forsome cells in the page is indeterminate and cannot be
resolved to a 0 or 1.

The Solution
Traditional solutions to prevent this would involve
retaining the power to the drive for sufficient time toallow the page program operation to complete. This
could be achieved through on-board power hold-up
capacitors to provide enough charge for the page
program time, plus some program latency. If the drive
being used had a DRAM cache, then the amount of
stored energy would need to be significantly higher toprevent the cache contents from being lost.

Recent advances in memory architecture have enabled
a new class of 3D NAND based solid state storage
solutions that have eliminated the paired page issue.
3D NAND uses vertically stacked memory cell layersthat can provide the same endurance as planar NAND
flash with increased cost effectiveness and faster
performance.
With Greenliant’s new industrial 3D MLC NAND based
NANDrive™ devices, programming can now be achievedin a single pass where both pages are programmed
at the same time. A representation of single-passprogramming below shows the classic threshold voltage(Vt) distribution of cells in MLC NAND and how thecharge state is decoded to the bit values for those cells.

Representation of single-pass programming

The upper and lower pages within a block can now be
sequentially programmed by a NAND flash controller
in one operation so the cell charge is moved to therequired level for both pages simultaneously, effectively
eliminating the possibility of data corruption in paired
pages during power interrupts. Only the current page
being written is at risk and this can be managed by atransaction failsafe host file system.

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NANDrive™ Power Interrupt Data Protection
Advanced Features
With 3D MLC NAND’s single-pass programming feature,
the controller programs all states in a single step without
disturbing adjacent cells and reducing the risk to data
already in place on the drive (called “data at rest”).
Furthermore, to retain data that could otherwise be lost
due to program-and-erase errors, the controller may
periodically update 3D NAND memory cells.
An intelligent controller, like those developed byGreenliant for use in its small form factor eMMC
NANDrive and SATA NANDrive BGA SSDs, will help
further minimize corruption of data in transition or in flight(in temporary DRAM or SRAM cache buffers) throughuse of advanced 3D NAND features. If the power fails

partway through the write operation, the host may typicallyuse journaling or some other transaction failsafe protocol
to determine that the last file written did not complete
and therefore the data in that file should be ignored orreplaced.
If the application uses small writes, which optimally shouldbe the size of a NAND page, then sophisticated controller
firmware will use advanced algorithms leveraging
automatic read calibration to try to recover the last
page, even if the power failed during the write operation.
Controller adaptive threshold voltage tuning further
enhances the ability of the controller to recover last pagedata.

Conclusion
These advances in controller and firmware design, coupled with new 3D NAND architectures, mean that there
is no longer the requirement for hold-up capacitors and voltage detection circuitry to prevent drive corruption
during a power failure. Greenliant’s advanced BGA SSDs with built-in power fail data protection are designed towithstand unstable power environments and are ideal for high reliability applications.

SATA NANDrive
145-ball BGA

eMMC NANDrive
100-ball BGA

eMMC NANDrive
153-ball BGA

Greenliant SATA and eMMC NANDrive SSDs with Power Fail Data Protection

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For more information, contact your Greenliant representative: www.greenliant.com/sales© 2020 Greenliant
These specifications are subject to change without notice. 07/2020
Greenliant, the Greenliant logo and NANDrive are registered trademarks or trademarks of Greenliant.