Provisioning Services 7.6 Getting started to Master Series VIII: Virtual disk access mode

virtual disks can exist in Provisioning server, file shares, or (in larger deployments) on storage systems that Provisioning server can communicate with (ISCSI, SAN, NAS, and CIFS). Virtual disks can be assigned to a single target device (proprietary image mode) or to multiple target devices (standard image mode).

After the virtual disk has been successfully created in the previous section, you can create the target device, but you must thoroughly understand the two different access modes of the virtual disk and the cache target location in the standard image mode prior to allocation. This section details the theoretical knowledge and configuration of virtual disk access patterns and cache destination locations. The default newly created virtual disk is a private image mode, such as:

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1.   Virtual Disk access mode

The virtual disk access mode options include:

• Standard image mode

• Private image Mode

1.1 standard image mode

Standard image mode allows users to push multiple target devices simultaneously from a single vdisk image through streaming technology, reducing the management overhead and storage requirements of virtual disks.

When you configure a virtual disk to use standard image mode, the virtual disk is set to read-only mode. Each target device then builds a write cache to store any data that the operating system needs to write. There are several write cache options available. Because the virtual disk is in read-only mode, the target device will always boot from a "clean" virtual disk each time it boots. If the computer is infected with a virus or spyware, the target device simply reboots the image.

When you update a virtual disk in standard image mode, the changes that are based on the vdisk image are captured into a differencing disk file (. aVHD) to build a new version of the base image. Each new version is still directly associated with the underlying image. Versioning allows you to capture these updates to a differencing disk for staging (maintenance, testing, production) before the update is available to production devices. If there is a problem with a version, you can easily restore that version. For more information about versioning, see Updating virtual disks .

Although each target device uses the same virtual disk, provisioning Services will still personalize the streaming image for each target device and provide the required information to ensure that the device is uniquely identifiable on the network. In addition, Provisioning Services provides a mechanism for assigning additional personalization settings to each device. This feature allows you to store application-specific values in the database and then retrieve unique values for the device when the target device is loaded. For more information, see Manage target device personalization settings .

1.2 Private Image Mode

A virtual disk in private image mode mimics the way a computer uses a regular hard drive in a very approximate manner. That is, only one target device can use a private image virtual disk at any one time .

Displays a private image virtual disk (read/write) assigned to a single production device, and a standard image virtual disk (read-only) that is assigned to a collection of production devices and shared by that collection. For standard image virtual disks, the write cache options include caching on the server disk, caching on the device's hard drive, or caching in device RAM.

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2.   Cache target location (standard image mode)

The following sections list and describe all the valid write cache destination location options:

• Caching on the device's hard disk

• Permanent cache on Device hard drive (experimental phase only)

• Caching in Device RAM

• Cache and overflow to the hard disk in device RAM (for Windows 7 and Server R2 (NT 6.1) and later)

• Caching on server disks

• Persistent caching on the server

2.1 Caching on the device's hard disk

The write cache can exist on the hard drive of the target device on the NTFS file format. This write cache option frees up space for Provisioning Server because there is no need to process write requests, and there is no limit to RAM.

The hard drive does not need to use any other software to enable this feature.

Note: unless the vdisk mode is set to private image mode, the write cache file belongs to the temporary file.

2.2 Permanent cache on device hard drive (experimental phase only)

This is the same as "cache on device hard disk", except that the cache is permanent. Currently, this write caching method is only an experimental feature and only supports NT6.1 or later (Windows 7 and Windows2008 R2 and later). Additionally, this method requires a different bootstrapper. To select the correct bootstrapper from the console, right-click on the provisioning Server and select Configure Bootstrapper . On the General tab, click the Boot file drop-down option, and then select CTXBP. BIN ". Citrix strongly recommends that the local HDD (client) drive have enough free space to store the entire virtual disk.

2.3 Cache in device RAM

The write cache can exist in the target device RAM in the temporary file mode. Memory access is always faster than hard disk access, so this caching method provides the quickest way to access the disk.

2.4 Cache and overflow to the hard disk on device RAM

This write cache method is in VHDX differencing format and applies only to Windows 7 and Server R2 (NT 6.1) and later:

• When the RAM space is zero, the target device write cache is written only to the local disk.

• When the RAM space is not zero, the target device writes to the cache and writes the RAM first.     When RAM is full, the earliest used data block is written to the local differencing disk to cache the updated data on RAM. The amount of RAM space specified is the non-paged kernel memory that the target device will occupy.

The VHDX chunked format has a faster file expansion rate than the "cache on device hard disk" mode. You should reconsider using the available local disk space to accommodate the streaming technology push workload. To ensure the reliability of target devices in high-demand workloads, Citrix recommends that the local disk free space be larger than the size of the virtual disk capacity.

If there is insufficient local disk space, the target device virtual disk IO goes into a paused state, waiting for more local disk free space to become available. This situation adversely affects workload continuity, so Citrix recommends allocating enough free space on the local disk.

The amount of RAM specified does not change the requirement for free space on the local disk. The more RAM is allocated, the more virtual disk IO is temporarily saved in the RAM cache before all data is rushed back to the VHDX file. RAM slows down the initial VHDX expansion speed.

2.5 caching on the server

The write cache can exist on Provisioningserver in a temporary file mode. In this configuration, all writes are processed by Provisioning Server, which can result in increased disk IO and network traffic.

For increased security, you can configure Provisioning Server to encrypt write cache files. Because the write cache file is stored on the hard drive between two reboots, the data should be encrypted to prevent the hard drive from being stolen.

2.6 Persistent caching on the server

Using this cache option allows you to save changes between reboots two times. When you use this option, the target device can retrieve changes that were made in the previous session that were different from the read-only vdisk image after rebooting. If the virtual disk is set to be permanently cached on the server , a device-specific writable disk file is automatically created for each target device that accesses the virtual disk. All changes made to the Vdisk image are written to the file, and the file is not automatically deleted when the computer is shut down.

The file name contains the MAC address and disk identifier of the target device, which uniquely identifies the target device. A target device can be assigned to multiple virtual disks, so multiple cache files will be associated.

To restore a virtual disk that uses the persistent cache on server mode, make sure that you back up all virtual disk files and associated user cache files before making any modifications to the vdisk.

The benefits of using this caching option include:

• Save the target device-specific changes made to the vdisk image.

• Has the same advantages as standard image mode.

Disadvantages of using this caching option include:

• This file can be used as long as the cache file remains valid. Any changes made to the virtual disk will force the cache file to be marked as invalid. For example, if you set the virtual disk to private image mode, all associated cache files will be marked as invalid.

Note: cached files that are marked as invalid are not automatically deleted, so you should manually delete these files on a regular basis.

Changes that invalidate files include the following:

• Placing a virtual disk in maintenance mode

• Placing the virtual disk in private image mode

• Mapping drives from the console

• Change the location of the write cache file

• Use Automatic Updates

3.   Configure virtual disks

3.1 Open PVS console-Virtual Disk pool-right-click the corresponding virtual disk and select Properties

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3.2 Cache type does not allow selection when selecting access mode for private image, default to "cache on server"

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3.3 When you choose the access mode of the standard image, you can modify the cache type according to the actual application, select the standard image access mode "permanently cache on the server" in this demo, click "OK"

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3.4 As shown in the following changes:

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The above is the virtual disk access mode, the target device cache location of the introduction and configuration, the entire configuration process is relatively simple, the focus is to understand the different ways in the actual environment of different applications.

This article is from the "Huang Jinhui column" blog, be sure to keep this source http://stephen1991.blog.51cto.com/8959108/1691901

Provisioning Services 7.6 Getting started to Master Series VIII: Virtual disk access mode