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AP-SDM004GAPANS-HTC Datasheet(PDF) 9 Page - List of Unclassifed Manufacturers |
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AP-SDM004GAPANS-HTC Datasheet(HTML) 9 Page - List of Unclassifed Manufacturers |
9 / 21 page SATA-Disk ModuleⅡ Ⅱ Ⅱ Ⅱ AP-SDMxxxxXPANS-HTX 8 © 2011 Apacer Technology Inc. Rev. 1.2 3. Flash Management 3.1 Error Correction/Detection The SDM implements a hardware ECC scheme, based on the BCH algorithm. It can detect and correct up to 8 bits or 15 bits error in 512 bytes. 3.2 Bad Block Management Although bad blocks on the flash media are already identified by the flash manufacturer, they can also be accumulated over time during operation. The SDM’s controller maintains a table that lists those normal blocks with disk data, the free blocks for wear leveling, and bad blocks with errors. When a normal block is detected broken, it is replaced with a free block and listed as a bad block. When a free block is detected broken, it is then removed from the free block list and marked as a bad block. During device operation, this ensures that newly accumulated bad blocks are transparent to the host. The device will stop file write service once there are only two free blocks left such that the read function is still available for copying the files from the disk into another. 3.3 Wear Leveling The NAND flash devices are limited by a certain number of write cycles. When using a FAT-based file system, frequent FAT table updates are required. If some area on the flash wears out faster than others, it would significantly reduce the lifetime of the whole SSD, even if the erase counts of others are far from the write cycle limit. Thus, if the write cycles can be distributed evenly across the media, the lifetime of the media can be prolonged significantly. This scheme is called wear leveling. Apacer’s wear-leveling scheme is achieved both via buffer management and Apacer-specific static wear leveling. They both ensure that the lifetime of the flash media can be increased, and the disk access performance is optimized as well. 3.4 Power Failure Management The Low Power Detection on the controller initiates crucial data saving before the power supplied to the device is too low. This feature prevents the device from crash and ensures data integrity during an unexpected power-off. |
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