Thank you erik for your quick response Is there any alternate way to use RTOS & SDFilesystem by which i can store large number of samples in to sd card. my Main intension of using RTOS is I would like to store 3200 samples / second from ADXL. As i have used tickers in previous version but limitation of higher data rates i was able to achieve 1600 samples using mbed tickers. Where tickers are serial way of execution. One after the other is being operated. Until 800 samples per second it works fine when it happens to go to 1600 and 3200 problem comes. So i decided to switch to RTOS so that it would be flexible enough to execute in threads. Can you please provide me any suggestion how to save data on to SD card using RTOS at regular interval of time? I.e. for every 10 sec i need to create a file and save the data in to it and after that another new file is created after every 10 secs.

Note that this libary does not increase the speed at which SDFileSystem operates. What it does do is make sure you can do other things while it is writing to the SD card. So if you spend 50% of your time writing to the SD card, and 50% of your time doing other stuff, it would definately help. If you spend 90% of your time writing to the SD card, it would do little.

You can have a look at: https://developer.mbed.org/users/neilt6/code/SDFileSystem/, which is improved version of regular SDFileSystem. Especially check if you can increase the SPI speed (an option in its constructor), which should help you.

Next in the SDFileSystem library, you got the FATFileSystem, with in there this file: https://developer.mbed.org/teams/mbed-official/code/FATFileSystem/file/e2ab678eb692/ChaN/ffconf.h. Now I have never checked this for the SDFileSystem! However for the USB flash drive library, which uses the same FATFileSystem, I could get a quite significant speed improvement by setting the last setting, FLUSH_ON_NEW_SECTOR to 0.

Thank you Erik for your suggestion and its working as per the suggestion you had provided me. By setting FLUSH_ON_NEW_SECTOR to 0 speed of the saving data has been increased and i am able to store 3200 samples. But i did not get any clue of how its happening. I have one more question that will there be an effect if i do the setting as you had suggested further in future. Thank you.

To be fair: I also don't know exactly why it works as it works. I enabled debug statements when I looked at it for the USB flash drive library, and what I saw was that if you wrote a large file with that setting enabled (as default), it would after each sector it wrote, read other sectors (probably with file system information), and then write the next sector, etc. While when disabled, it would simply write all sectors consecutively without (many) read operations in between. Only when the file was closed and/or a new one was opened it would update the other sectors with where I assume was filesystem and directory information.