Disk Alignment – OS Test

In a SAN environment, the smallest hardware unit used by a SAN storage array to build a LUN out of multiple physical disks is called a chunk or a stripe. To optimize I/O, chunks are usually much larger than sectors. Thus, a SCSI I/O request that intends to read a sector in reality reads one chunk.

On top of this, in a Windows environment, NTFS is formatted in blocks ranging from 1MB to 8MB. The file system used by the guest operating system optimizes I/O by grouping sectors into so called clusters (allocation units).

Figure 2 shows these three layers at issue. There are the SAN blocks at the bottom, then the VMFS blocks in the middle, and then the NTFS blocks used by the Windows VM.

Figure 2 : The SAN, VMFS, and NTFS blocks

If these three layers are not aligned, your SAN may be working harder than it needs to. For example, a call to read a single NTFS block may require the SAN to read three blocks as shown below:

Figure 3 : Unaligned partitions

An unaligned partition therefore, results in a track crossing and an additional I/O, incurring a penalty on latency and throughput. The additional I/O (especially if small) can impact system resources significantly on some host types.

What would hence be ideal is for the three layers in Figure 4 above to be aligned so that a single NTFS block requires only one SAN block to be read as illustrated below:

Figure 4 : Aligned partitions

An aligned partition ensures that the single I/O is serviced by a single device, eliminating the additional I/O and resulting in overall performance improvement.

Therefore, whenever users to Windows VMs complaint that the VM is running slower than usual, you may want to check the disk alignment to determine whether the slowdown can be attributed to one/more unaligned disk partitions. This test enables you to perform such a check.

This test is disabled by default. To enable the test, go to the enable / disable tests page using the menu sequence : Agents -> Tests -> Enable/Disable, pick Oracle VM Server as the desired Component type, set Performance as the Test type, choose the test from the disabled tests list, and click on the < button to move the test to the ENABLED TESTS list. Finally, click the Update button.

Target of the test : Oracle VM Server

Agent deploying the test : A remote agent

Outputs of the test : One set of results for each disk partition on each Windows VM of the Oracle VM Server being monitored.

Configurable parameters for the test
Parameters	Description
Test Period	How often should the test be executed.
Host	The host for which the test is to be configured.
Port	The port at which the specified Host listens. By default, this is NULL.
Oracle VM Manager, Oracle VM Manager User, Oracle VM Manager Password, and Confirm Password	This test remotely connects to the Oracle VM Manager that manages the monitored Oracle VM Server and uses the web services API of the Oracle VM Manager to pull out metrics of interest. To enable this test to communicate with the web services API, you first need to configure the test with the IP address or host name of the Oracle VM Manager. This can be done using the Oracle VM Manager text box. Then, you need to configure the test with the credentials of a user with Admin rights to the Oracle VM Manager. Use the Oracle VM Manager User and Oracle VM Manager Password parameters to configure these credentials. Finally, confirm the password by retyping it in the Confirm Password text box.
SSL	By default, the Oracle VM Manager is SSL-enabled. Accordingly, the SSL flag is set to Yes by default. This indicates that the eG agent will communicate with the Oracle VM Manager via HTTPS by default.
WebPort	By default,, the Oracle VM Manager listens on 7002. This implies that while monitoring an Oracle VM server via an SSL-enabled Oracle VM Manager, the eG agent, by default, connects to port 7002 of the Oracle VM Manager to pull out metrics. In some environments however, this default port may not apply. In such a case, against the WebPort parameter, you can specify the exact port at which the Oracle VM Manager in your environment listens so that the eG agent communicates with that port.
Exclude VMs	Administrators of some virtualized environments may not want to monitor some of their less-critical VMs - for instance, VM templates - both from 'outside' and from 'inside'. The eG agent in this case can be configured to completely exclude such VMs from its monitoring purview. To achieve this, provide a comma-separated list of VMs to be excluded from monitoring in the Exclude VMs text box. Instead of VMs, VM name patterns can also be provided here in a comma-separated list. For example, your exclude vms specification can be: xp,lin,win,vista. Here, the * (asterisk) is used to denote leading and trailing spaces (as the case may be). By default, this parameter is set to none indicating that the eG agent obtains the inside and outside views of all VMs on a virtual host by default. By providing a comma-separated list of VMs/VM name patterns in the Exclude VMs text box, you can make sure the eG agent stops collecting 'inside' and 'outside' view metrics for a configured set of VMs.
Ignore VMs Inside View	Administrators of some high security Oracle environments might not have permissions to internally monitor one/more VMs. The eG agent can be configured to not obtain the 'inside view' of such ‘inaccessible’ VMs using the Ignore VMs Inside View parameter. Against this parameter, you can provide a comma-separated list of VM names, or VM name patterns, for which the inside view need not be obtained. For instance, your ignore vms inside view specification can be: xp,lin,win,vista. Here, the * (asterisk) is used to denote leading and trailing spaces (as the case may be). By default, this parameter is set to none indicating that the eG agent obtains the inside view of all VMs on an Oracle VM server by default. Note: While performing VM discovery, the eG agent will not discover the operating system of the VMs configured in the ignore vms inside view text box.
Inside View Using	By default, this test communicates with every VM remotely and extracts “inside view” metrics. Therefore, by default, the inside view using flag is set to Remote connection to VM (Windows). Typically, to establish this remote connection with Windows VMs in particular, eG Enterprise requires that the eG agent be configured with domain administrator privileges. In high-security environments, where the IT staff might have reservations about exposing the credentials of their domain administrators, this approach to extracting “inside view” metrics might not be preferred. In such environments therefore, eG Enterprise provides administrators the option to deploy a piece of software called the eG VM Agent (Windows) on every Windows VM; this VM agent allows the eG agent to collect “inside view” metrics from the Windows VMs without domain administrator rights. To ensure that the “inside view” of Windows VMs is obtained using the eG VM Agent, set the inside view using flag to eG VM Agent (Windows). Once this is done, you can set the Domain, Admin User, and Admin Password parameters to none.
Ignore WINNT	By default, the eG agent does not support the inside view for VMs executing on Windows NT operating systems. Accordingly, the Ignore WINNT flag is set to Yes by default.
Domain, Admin User, Admin Password, and Confirm Password	By default, this test connects to each virtual guest remotely and attempts to collect “inside view” metrics. In order to obtain a remote connection, the test must be configured with user privileges that allow remote communication with the virtual guests. The first step towards this is to specify the Domain within which the virtual guests reside. The admin user and admin password will change according to the domain specification. Discussed below are the different values that the domain parameter can take, and how they impact the admin user and admin password specifications: If the VMs belong to a single domain: If the guests belong to a specific domain, then specify the name of that domain against the Domain parameter. In this case, any administrative user in that domain will have remote access to all the virtual guests. Therefore, an administrator account in the given domain can be provided in the Admin User field and the corresponding password in the Admin Password field. Confirm the password by retyping it in the Confirm Password text box. If the guests belong to different domains - In this case, you might want to provide multiple domain names. If this is done, then, to access the guests in every configured domain, the test should be configured with the required user privileges; this implies that along with multiple Domain names, multiple Admin User names and Admin Passwords would also have to be provided. To help administrators provide these user details quickly and easily, the eG administrative interface embeds a special configuration page. To access this page, simply click on the Click here hyperlink that appears just above the parameters of this test in the test configuration page. If the inside view using flag is set to ‘eG VM Agent (Windows)’ - In this case, the inside view can be obtained without domain administrator privileges. Therefore, set the Domain, Admin User, and Admin Password parameters to none. If the guests do not belong to any domain (as in the case of Linux/Solaris guests) : In this case, specify "none" in the Domain field, and specify a local administrator account name in the Admin User below. Prior to this, you need to ensure that the same local administrator account is available or is explicitly created on each of the virtual machines to be monitored. Then, proceed to provide the password of the Admin User against Admin Password, and confirm the password by retyping it in the Confirm Password text box. If key-based authentication is implemented between the eG agent and the SSH daemon of a Linux guest, then, in the Admin User text box, enter the name of the user whose <USER_HOME_DIR> (on that Linux guest) contains a .ssh directory with the public key file named authorized_keys. The admin password in this case will be the passphrase of the public key; the default public key file that is bundled with the eG agent takes the password eginnovations. Specify this as the admin password if you are using the default private/public key pair that is bundled with the eG agent to implement key-based authentication. On the other hand, if you are generating a new public/private key pair for this purpose, then use the passphrase that you provide while generating the pair. For the detailed procedure on Implementing Key-based Authentication refer to the Monitoring VMware Infrastructures document. If the guests belong to different domains - In this case, you might want to provide multiple domain names. If this is done, then, to access the guests in every configured domain, the test should be configured with the required user privileges; this implies that along with multiple Domain names, multiple Admin User names and Admin Passwords would also have to be provided. To help administrators provide these user details quickly and easily, the eG administrative interface embeds a special configuration page. To access this page, simply click on the Click here hyperlink that appears just above the parameters of this test in the test configuration page. If the inside view using flag is set to ‘eG VM Agent (Windows)’ - In this case, the inside view can be obtained without domain administrator privileges. Therefore, set the domain, admin user, and admin password parameters to none.
DD Frequency	Refers to the frequency with which detailed diagnosis measures are to be generated for this test. The default is 1:1. This indicates that, by default, detailed measures will be generated every time this test runs, and also every time the test detects a problem. You can modify this frequency, if you so desire. Also, if you intend to disable the detailed diagnosis capability for this test, you can do so by specifying none against DD frequency.
Detailed Diagnosis	To make diagnosis more efficient and accurate, the eG Enterprise embeds an optional detailed diagnostic capability. With this capability, the eG agents can be configured to run detailed, more elaborate tests as and when specific problems are detected. To enable the detailed diagnosis capability of this test for a particular server, choose the On option. To disable the capability, click on the Off option. The option to selectively enable/disable the detailed diagnosis capability will be available only if the following conditions are fulfilled: The eG manager license should allow the detailed diagnosis capability Both the normal and abnormal frequencies configured for the detailed diagnosis measures should not be 0.

Measurements made by the test

Measurement

Description

Measurement Unit

Interpretation

Disk partition alignment status

Indicates whether this disk partition is aligned or not.

If the partition is unaligned, this test reports the value Partition is not aligned. For an aligned partition, this test reports the value Partition is aligned.

The numeric values that correspond to the above-mentioned measure values are described in the table below:

Measure Value	Numeric Value
Partition is aligned	100
Partition is not aligned	0

Note:

By default, this measure reports one of the Measure Values listed in the table above. The graph of this measure however will represent the disk alignment status using the numeric equivalents - 100 or 0.

If a partition is found to be misaligned, you can use the detailed diagnosis of this test to figure out the caption, device ID, logical partition name, and block size of the faulty partition.