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Re: nand flash



I've ported NetBSD to Mesa Electronics 4C81 PC104plus SBC.  The storage
is 32MB/64MB bare NAND which holds BSDFFS.

How do you handle the bad blocks that develop as the device "wears" ?

Could LFS be more appropriate for 'wear levelling' ?
Especially now that we can use it as root filesystem...

// Yocto


----- Original Message ----- From: "Toru Nishimura" <locore64%alkyltechnology.com@localhost>
To: <tech-embed%netbsd.org@localhost>
Sent: Thursday, October 04, 2007 10:00 PM
Subject: Re: nand flash


David Young  asked;

but the decision was made weighing "the rootfs is
seldom written beyond configuration mods by administrators." Software ECC is always calc'ed and verified, block write is counted and recorded inside
NAND spare fields.

How do you handle the bad blocks that develop as the device "wears" ?

The answer is "by manual intervention," just like good-old-days Winchester
style hard disk drive bad sector management practice.  I wrote a cmdline
tool to manage bad block list and relocate block contents. In principle we
neglect the whole NAND woe/buzz to happen due to the above mentioned
rational. "this tools may cause hazardous results to hurt you, trained service
personel only, or don't use this."

If I have chose MMC/SD/CF media to go, I would build vnd on a large file
on the FAT filesys and forget how good/bad to gauge badblock and
wear-leveling schemes inside.

Toru Nishimura/ALKYL Technology





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