Hi,
I posted this in QNX4 community, they ask me to repeat in QNX 6.

I encounter a problem that using cp command to copy a large file (~1GB size) from USB to SD card or vise versa. during 
copying, error out and root directory is gone (/ mount point is umounted).

The following is verbose from cp:
cp: LSTAT(/dos/d/,buf)
cp: LSTAT(/log/file.121,buf)
cp: copy_guy(/log/file.121,/dos/d///file.121)
cp: OPEN(/log/file.121,0,0)
cp: OPEN(/dos/d///file.121,2401,100640)
cp: LSTAT(/dos/d///file.121,buf)
cp: Copying /log/file.121 to /dos/d/file.121
cp: write  (/dos/d///file.121): Input/output error
cp: ERRS++ (1) write()
 88.74% (755840/851673 kbytes, 2323 kb/s)
cp: read   (/log/file.121): Bad file descriptor
cp: ERRS++ (2) read()
cp: past_data_copy errs_in =0, errs = 2
cp: exit_copy_guy (rc=0)
cp: CLOSE(fildes)
cp: close  (/log/file.121): Bad file descriptor
cp: ERRS++ (3) _close()
cp: CLOSE(fildes)
cp: close  (/dos/d///file.121): Bad file descriptor
cp: ERRS++ (4) _close()

QNX version: 6.4.1
both SD card and usb key is running on USB bus. I can see during copy devb-umass and io-usb processes are taking CPU 
usages

what could be the root cause of this?

Thanks in advance.