giving room for Linux filesystems on MLC/SLC

[Tadimarri Sarath Babu]

----- Original Message ----- 
From: "Artem Bityutskiy" <dedekind1 at gmail.com>
To: "Emmanuel Michon" <emmanuel.michon at polytechnique.org>
Cc: <linux-mtd at lists.infradead.org>
Sent: Tuesday, October 20, 2009 6:09 PM
Subject: Re: giving room for Linux filesystems on MLC/SLC


> On Tue, 2009-10-20 at 12:56 +0200, Emmanuel Michon wrote:
>> Hello,
>>
>> we're preparing in my company the software for a general purpose (.5K,
>> 2K, 4KB page)
>> hardware MLC/SLC controller, especially how we're going to
>> choose the byte offsets of a page+spare for `metadata' and `bad
>> blocks' (those are excluded by our ECC check hardware).
>>
>> 0                                               4096+epsilon
>> | metadata | data | bb info | data
>>
>> Our primary goal is to be compatible with our proprietary filesystem,
>> but if we can enable Linux family of MTD FS with little effort, let's
>> prepare it
>>
>> `bad block' information is a hardware stuff (unconsistently, poorly)
>> documented to be near the start of spare area.
>>
>> For some reason we have this 4 byte metadata at the start of each
>> page. Does this software concept apply to ubifs and friends and should
>> it be sized differently?
>
> We work with an abstract flash mode: it consists of eraseblock, each
> eraseblock has several min. I/O units. So if in your cases the driver
> hides these meta-data bytes, it should be fine.
>
> However, current UBIFS is hard-coded with an assumption that min. I/O
> size is power of 2. This would probably have to change. There was no
> fundamental reason why we did it like this, we just wanted to save some
> CPU cycles and avoid divisions. But this can be changed.
>
>> Btw, any success stories about UBIFS+MLC since the FAQ report on this topic?
>
> I have not heard them.

I have recently tested UBI/UBIFS using "fsstress" command with linux-2.6.28 kernel on FlexOneNAND
over 256 MB MLC partition.
The test has run fine for 4 days continuosly.

I used the following command line parameters for the fsstress.
fsstress -p 3 -n 10000 -d /tmp -l 0

I have a plan to test the UBI/UBIFS on latest linux-2.6.31 kernel . Will let you know the results
once it is done.

Regards,
Sarath.