One of the great features that the Blobs Service in Azure provides, is the ability to create snapshots for a given blob.
In the following I will elaborate on how to create a snapshot and how to get all the snapshots for a given blob.
Needless to say that snapshot make the application more robust and has the ability to add “transaction” behavior when manipulating the blob data (point of failure return to base blob).
Another useful case could be creating a snapshot to a cloud drive (mounted as NTFS to a blob) and restoring/imaging when needed.

Creating a snapshot

First lets access the storage service

(Note that the code samples are using the Microsoft.WindowsAzure.StorageClient namespace)

string connectionString = String.Format("DefaultEndpointsProtocol=https;AccountName={0};
AccountKey={1}",storageInfo.StorageName, storageInfo.PrivateKey);

            CloudStorageAccountaccount = CloudStorageAccount.Parse(connectionString);

blobClient = account.CreateCloudBlobClient();

Get a reference to blob

CloudBlob baseblob=blobClient.GetBlobReference("testcontainer/baseblob.txt");

Create a snapshot of the blob

CloudBlob snapshot = baseblob.CreateSnapshot();

Let verfy that we managed to create a snapshot using Cloud Storage Manger:



When creating the snapshot the blob returned holds a Snapshot property of type DateTime that can be used for future access.

DateTime timestamp = (DateTime)snapshot.Attributes.Snapshot;

I can use the timestamp to get a reference to the snapshot in the following way:

CloudBlob snapshot2 = new CloudBlob("testcontainer/baseblob.txt", timestamp, blobClient);

List all snapshots

Getting all the snapshot for given blob is a bit more tricky since a snapshot blob is referred as an ordinary blob in the blobs service.
The only hint is the parameter SnapshotTime in the blob that can indicate if it’s a regular blob or snapshot one.

So I will need to traverse all the blobs in the container and collect only the blobs that are typed as snapshots and has the URI to my base blob.

BlobRequestOptions options = new BlobRequestOptions()

            {

                BlobListingDetails = BlobListingDetails.Snapshots,

                UseFlatBlobListing = true

            };

IEnumerable<IListBlobItem> items = blobClient.GetContainerReference("testcontainer").ListBlobs(options);

items.Where(item=> ((CloudBlob)item).SnapshotTime.HasValue&& item.Uri.Equals(baseblob.Uri));

Point of interest

On of the cool feature Cloud Storage Manager offers is the ability to create and restore snapshot for an entire directory in the Azure blob service.

Recent announcement from MS indicates that Azure storage (blobs/tables/queues) rate will decreased from 0.15$ GB Per Month to 0.14$ GB per Month.

Just to feel the numbers for 1TB we will receive a discunnt of 10$ (0.15$GB/Month*1000 -0.14$GB/Month = 10$).

Moreover MS provides additional discounts on storage account that is more than 1TB as describes in the following table:

As you might know performance counters are well known and categories.

By just opening perfmon.exe on the local windows machine you can view lots of counters that concealed endless of information regarding the main components and resources of your OS (CPU, Memory, Network etc..).

Since my application is deployed in the cloud monitoring can be tricky.

Well I can always do remote desktop to my role instance (check the following blog on RDP in Azure ) and launch perfmon.

Now image that you have 10 machines (scattered around the world each doing something else) RDP each one can be time demanding task.

Moreover as you might know Azure diagnostics enables to save the performance counters guttered into a predefined storage account.

The data is accessibly and persistence but finding the problems just by queering the table wont reveal any problem because of the huge amount of data guttered.

Luckily Spotlight on Azure has a great feature that enables to configure remotely performance counters and get aggregations capabilities from the role instance level up to the deployment level. One can compare the counters graphs over time and easily spot problems.

So let’s get started

After choosing the role instance from the tree view navigate to the Custom tab.

Here you can view the current pre-defined counters that ships with the product. just by viewing those counters lots of insights can be deducted on your instance/role/deployment.

For this demonstration I am interesting in testing the behavior of the Web Role Asp.Net application.

Currently my web role is responding to frequent user calls. My goal is to analyze the Asp.Net web application performance.

Configuring the counters:

1. Press the Configure button.
   
2. From the performance categories select Asp.Net application.
   
3. Add the following counters:

• ASP.NETApplications - Requests/Sec – any low value than the amount of request generated per seconds is queue in the server
  other than that this counter is very important in order to measure the rate a witch requested are handled.
• ASP.NETApplications - Request Execution Time – in milliseconds that takes to render the last requested page and then transmit it to the user. Load testing can easily show how the time of processing the execution of a request can be increased.
• ASP.NETApplications – Session total – current sessions opened. Usually the number of session is closed after 20 minutes. But the general count is by the cookies of the users.

    Lets view the data:

correlating the network counter with counters from other categories can show how well the machine function.

For example selecting the Processor User time % can show the CPU utilization against the Web server operations

Finishing our discussion any custom created counters (performance counter create by code using the diagnostics assembly in .net) can also be added for monitoring using Spotlight on Azure.

from the configuration window check the following: