XenCenter

Storage Read Caching

September 26, 2024

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Read Caching improves a VM’s disk performance as, after the initial read from an external disk, data is cached within the host’s free memory. It greatly improves performance in situations where many VMs are cloned off a single base VM as it drastically reduces the number of blocks read from disk. For example, Read Caching improves performance in Citrix Virtual Desktops Machine Creation Services (MCS) environments.

This performance improvement can be seen whenever data must be read from disk more than once, as it gets cached in memory. This performance difference is most noticeable in the degradation of service that occurs during heavy I/O situations. For example:

When a significant number of end users boot up within a narrow time frame (boot storm)
When a significant number of VMs are scheduled to run malware scans at the same time (antivirus storm)

Note:

The amount of memory assigned to the XenServer control domain (dom0) might need to be increased for the most efficient use of read caching. For instructions on increasing dom0 memory, see Changing the Control Domain Memory.

XenCenter displays the status of Read Caching on the VM’s General tab.

Note:

Storage Read Caching is available for XenServer Premium Edition customers.

Read Caching is enabled by default, provided:

The XenServer host is licensed with XenServer Premium Edition.
The VM is attached to a VDI on a file-based SR such as NFS, EXT3/EXT4, or GFS2. Read Caching cannot be used with other SR types.
The VM is created from a fast clone or a snapshot, or the VM is attached to a read-only VDI.

For detailed information about Read Caching, see Storage read caching.

To disable read caching

You can disable read caching for an SR in its Properties dialog.

In the Resources pane, select the SR that you want to disable read caching on.
In the General tab, click Properties.
In the Properties dialog, deselect Enable Read Caching.
Click OK.

To enable read caching

You can enable read caching for an SR in its Properties dialog.

In the Resources pane, select the SR that you want to enable read caching on.
In the General tab, click Properties.
In the Properties dialog, select Enable Read Caching.
Click OK.
Restart any VMs that you want to benefit from the changed setting.

XenServer 8

Storage read caching

Citrix Hypervisor 8.2 Cumulative Update 1

Storage read caching

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Storage Read Caching

September 26, 2024

Contributed by:

September 26, 2024

Contributed by:

Storage Read Caching

To disable read caching

To enable read caching

Related documentation

XenServer 8

Citrix Hypervisor 8.2 Cumulative Update 1

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