MTD F8 Manuel d'utilisateur

Copyright 2009, Toshiba Corporation.Evaluation of UBI and UBIFSTOSHIBA CORPORATIONCore Technology CenterEmbedded System Technology Development Dept.UW

10Topic 2 : Flash space overhead• The factor of UBIfor BadBlock(changeable bykernel config(default 1 % = 20PEB)usedusedreservedreservedreservedreserve

11Topic 2 : Flash space overhead• The factor of UBIFSreserved by UBINAND (MTD 32MB, UBI 1 volume)2024 EBs24 EBsSuperblock/Masterblock (3)Log/LPT/... (

12• The actual total size of user dataConditions:– MTD partition size: 32MB, UBI volume number: 1– LZO compression enable– Random Data Random Data (Th

13• Typical Data BlockLEB 893 lprops: free 3072, dirty 368 (used 12432), flags 0x0UBIFS(2024 EBs)Main Area (2007 EBs)4For Internal-Vol,Wearleveing, Sc

14Topic 2 : Flash space overhead• Cause Free space at the tail of PEBhttp://www.linux-mtd.infradead.org/doc/ubifs.html#L_spaceacc“Flash space accounti

15Topic 3 : UBI scrubbing on preempt kernel• UBI “Scrubbing” function– When a bit-flip (ECC 1 bit error) is detected in a physical erase block, the bl

16Topic 3 : UBI scrubbing on preempt kernel• Patch– The lock of LEB is released before queuing a scrubbing. – It is not necessary to hold the lock whe

17Topic 4 : Sub-page write verify• MTD NAND “Verify NAND page writes” function– is the write verify function per a NAND physical page.– is implemented

18Topic 4 : Sub-page write verify• PatchThe function for write verifying with column (offset) and size is added to MTD NAND structure in MTD NAND driv

19Topic 4 : Sub-page write verify[drivers/mtd/mtd/nand/nand_base.c]static int nand_do_write_ops(struct mtd_info *mtd, loff_t to,struct mtd_oob_ops *op

2Agenda• Background• Topic1. Boot time2. Flash space overhead3. UBI scrubbing on preempt kernel4. Sub-page write verify5. Error handling• Summary• Ref

20Topic 5 : UBIFS/UBI error handling• UBIFS became read-only when an error occurs. – for protect data from any further corruption– http://www.linux-mt

21Summary• Boot Time– The initializations time of MTD NAND driver and UBI depends on the size.• The optimization of building BBT in MTD driver and rea

22References– MTD, JFFS2, UBIFS, UBIhttp://www.linux-mtd.infradead.org/– YAFFS2http://www.yaffs.net/– LogFShttp://www.logfs.com/logfs/– CE Linux Forum

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3Background• Large size NAND flash memory is commonly used in embedded systems & Flash File systems for Larger size NAND are necessary.• UBI : U

4BackgroundNAND NOR DataFlash AG-AND OneNAND ECC’dNORMTD device, MTD APIVFSJFFS2 YAFFS2 LogFS UBIFSUBIBlockDeviceHDDSystem Call I/FFlash memoryVFS: Vi

5Background• Software– Linux kernel : Vanilla kernel 2.6.20.19 + Original patch for embedded systems– UBIFS / UBI : Vanilla kernel 2.6.30– MTD

6Topic 1 : Boot timeThe correlation between the time and the sizeMTD 32MB partition, UBI 1 volume (Toshiba NAND)0100200300400500600700800900MTD 32 MB

7Topic 1 : Boot timeThe MTD NAND driver initialization is slow.The time is not depend on the size of MTD partition, is depend on the size of NAND chip

8Topic 1 : Boot timeThe UBI initialization is slow.The time is depend on the size of MTD partition.• CauseThe reading of EC (Erase Counter) and VID (V

9Topic 2 : Flash space overhead• Problem“df” command reports too few free space.The result of df on 32 MB (32768 1k-blocks) MTD partition...• Factors“