Ext2 Filesystem

[sandeepyy]

Hi ALL,

I am currently working on Ext2 file-system on SLC NAND Flash device. I have added code which increments the erase/write count at sector level on NAND Flash device. So when ever there is a write or erase then this is increment the respective erase_count array and write count array respectively.

I have created 3 test applications with below algorithm with different write/read sizes:

#define MAX_COUNT 50
Counter =0;
Loop1:mount();
Write_all();//open file, write data to NAND, close.
Umount();
Mount();
Read_all();//open a file, read data from NAND, close.
Umount();
While(counter++ < MAX_COUNT) Loop1;

1) testAP1-25KB write/read- Loop for 256 times to write 64MB file
2) testAP2-1MB write/read-Loop for 64 times to write 64MB file
3) testAp3-2MB write/read-Loop for 32 times to write 64MB file

Below is erase/write count for Filesystem data at Sector 0:
with testAP1: erase/write count =240
testAP2: erase/write count=203
testAP3:erase/write count=250


Can any one please tell me having different write/read sizes in Test application will have any affect on the Filesystem block updates?
What is the pattern/logic behind this?
For this kind of behaviour where do I have to look in?

Any suggestion would be appreciated.

Many Thanks,
Sandeep Yedire

[Rubberman]

Has the device been mounted with, or without, the sync option?

[sandeepyy]

The device is mounted without sync option.

[Rubberman]

Are you sure that this variable is incremented on a physical write, or is it just incremented when the kernel gets a write command?

[sandeepyy]

Yes I am sure, I have added increment count code in "./drivers/mtd/nand/".

[Rubberman]

That is, when the physical block is actually re-written?

[sandeepyy]

This based on PDflush deamon. This is based on 30sec max limit and Dirty pages > 10% active memory.
Then physical block is being erased and updated with new data. Please not this ratio we are noticing for filesystem block at sector 0.

[Rubberman]

Well, to get back to your original questions

1. Can any one please tell me having different write/read sizes in Test application will have any affect on the Filesystem block updates?
2. What is the pattern/logic behind this?
3. For this kind of behaviour where do I have to look in?

Answers:
1. You will need to do some experimentation here to tell unless you can determine the answer from source code analysis.
2. Don't know.
3. Don't know.

Helpful (not!) I know. Sorry, but I think you are ahead of me on analyzing this behavior.