Programming FSRM quotas


Recently I was evaluating the options I had for implementing disk quotas on a backend system running on a major Internet Service Provider in Brazil.

Windows offers quota management up to some degree since NTFS 5 (Windows 2000) with user/volume quotas. Those were not appropriate for our scenario since we needed to set quotas on a per directory basis and this was not supported natively by Windows until the arrival of Windows Server 2003 R2.

R2 brings us a new feature called File Server Resource Manager a.k.a. FSRM. It is exposed for the system administrator as an MMC 3.0 snap-in.

Unfortunately, as of today Microsoft does not officially support any way for programming against FSRM quotas.  I said “officially support” because if the snap-in can do it, probably we can too! So after some research I found two DLLs called srm.dll and srmlib.dll that happens to do the stuff we want. Srm.dll exposes FSRM functionality through COM and srmlib.dll is a managed code wrapper around srm.dll.

Let’s take a look at some sample code:

using System;

using System.Collections.Generic;

using System.Text;

using Microsoft.Storage;

using System.IO;

using System.Runtime.InteropServices;


namespace Fsrm {

    class Program {

        static void Main(string[] args) {

            string directoryName = @"c:FsrmTests";


            // Creates a directory for testing if necessary

            if (!Directory.Exists(directoryName)) {




            ISrmQuotaManager quotaManager = new SrmQuotaManagerClass();

            ISrmQuota quota = null;

            try {

                // Try to get quota info

                quota = quotaManager.GetQuota(directoryName);

                quota.QuotaLimit *= 2;


            catch (COMException ex) {

                unchecked {

                    if (ex.ErrorCode == (int)0x80045301) {

                        // Quota doesn’t exist for this directory. Create it.

                        Console.WriteLine("No quota defined for ‘{0}’. Creating quota.", directoryName);

                        quota = quotaManager.CreateQuota(directoryName);

                        quota.QuotaLimit = 1024 * 1024;


                    else {







            // Update quota info



            // Add new file to the diretory to see QuotaUsed getting updated

            File.WriteAllText(directoryName + @"" + Path.GetRandomFileName() + ".txt", "Testing FSRM directory quotas");

            Console.WriteLine("New file added. Quota doubledrn{0} of {1} used.", quota.QuotaUsed, quota.QuotaLimit);





This sample doubles the size of the directory’s quota and puts a file in it every time it is run.

There are a bunch of other classes and methods available. Have fun!

This thing still has some bugs

It looks like my plans on becoming a multi-billionaire referring links to Amazon have failed. 😛

Today I tried to include another book on my list, but the site simply started to generate wrong URLs.

Another bug that bothers me is the fact from time to time the lists don’t render correctly:

Let’s hope these bugs are fixed as soon as possible.