Description of problem:
See the following code:
max_ret = 0;
		for (i = 0; i < finfo->stripe_count; i++) {
			memset(buf[i], 0, 4096);  <---- here
			ret = read(finfo->fd[i], buf[i], 4096);
			if (ret > max_ret)
				max_ret = ret;
		}
		for (i = 0; i < max_ret; i++)
			for (j = 0; j < finfo->stripe_count; j++)
				newbuf[i] |= buf[j][i];
			write(target, newbuf, max_ret);


There is no need to memset the whole 4K, we are reading from the file, writing as much as needed to it.
You should memset (4096 - ret) after reading.