mkfile.js

var fs = require('fs');
var crypto = require('crypto');

var dirName = './files';
var before = Date.now();
var mkfileNum = 5000;

// mkdir
fs.exists(dirName, function(exists) {
    if (!exists) {
        fs.mkdir(dirName, function(err) {
            if (err) throw err;
            console.log('dir created', dirName);
            mkfiles(0);
        });
    } else {
        mkfiles(0);
    }
});

function mkfiles(n) {
    if (n < mkfileNum) {
        var s = Date.now() + ':' + n;
        var d = crypto.createHash('sha1').update(s).digest('hex');
        console.log('now=', n, 'data=', d);
        fs.writeFile(dirName + '/' + d + '.log', d, function(err) {
            if (err) throw err;
            fs.close
            mkfiles(n+1);
        });
    } else {
        console.log('complete, ', Date.now() - before);
    }
}

mkfile2.js

var fs = require('fs');
var crypto = require('crypto');
var cp = require('child_process');

var dirName = './files';
var before;
var ulimit = 0;
var mkfileNum = 5000;

// mkdir
fs.exists(dirName, function(exists) {
    if (!exists) {
        fs.mkdir(dirName, function(err) {
            if (err) throw err;
            console.log('dir created', dirName);
            reqLimit();
        });
    } else {
        reqLimit();
    }
});

function reqLimit() {
    cp.exec('ulimit -n', function (error, stdout, stderr) {
        if (error !== null) {
            console.log('exec error: ' + error);
        } else {
            ulimit = parseInt(stdout, 10);
            console.log('ulimit=', ulimit);

            before = Date.now();
            mkfiles(0);
        }
    });
}

var wrote = 0;
function mkfiles(n) {
    if (n < mkfileNum) {
        if ((n - wrote) >= ulimit-12) {
            // 超えてたら次のtickへ
            setImmediate(function() {
                mkfiles(n);
            });
        } else {
            var s = Date.now() + ':' + n;
            var d = crypto.createHash('sha1').update(s).digest('hex');
            console.log('now=', n, 'data=', d);
            fs.writeFile(dirName + '/' + d + '.log', d, function(err) {
                if (err) throw err;
                wrote++;
            });
            mkfiles(n+1);
        }
    } else {
        console.log('complete, ', Date.now() - before);
    }
}