VMware GSX Server 2.5.2Features | Documentation | Knowledge Base | Discussion Forums You can use the Configuration Editor (Settings > Configuration Editor) to configure disks in one of three modes: persistent, undoable and nonpersistent.
The Configuration Editor on a Windows host shows an IDE virtual disk configured as undoable
The Configuration Editor on a Linux host shows installation of a SCSI virtual disk configured as persistent Disk modes determine how changes are saved to the disk. Raw, virtual and plain disks can use any available mode. For example, a user could have an undoable raw disk, an undoable virtual disk or an undoable plain disk. Disks in persistent mode are the simplest to use. Disks in persistent mode behave like conventional disk drives on your physical computer. All data written to a disk in persistent mode are written out permanently to the disk. The behavior is the same for all disk types. When you power off a virtual machine with a disk in undoable mode, any changes to the disk can be committed, saved until the virtual machine is powered on again or discarded. This is especially useful for experimenting with new configurations or unfamiliar software. Because of the disaster-recovery possibilities this mode offers, many users prefer to set disks in undoable mode as a standard part of their configurations. When data is written to an undoable mode disk, the changes are stored in a file called a redo log. A disk in undoable mode gives you the option later of permanently applying the changes saved in the redo log, so they become part of the main disk files. While the virtual machine is running, disk blocks that have been modified and written to the redo log are read from there instead of from the disk files. Any disk type can be used in undoable mode. When you power off a virtual machine with a disk in undoable mode, you are given three options:
If you choose to commit the redo log, the changes in the redo log are applied to the disk. The redo-log file is deleted. If you choose to discard the redo log, any changes in the redo log are not applied to the disk. The disk returns to the state it was in before changes began accruing in the redo log. If you choose to keep the redo log, the next time you power on the virtual machine GSX Server detects the redo-log file and prompts you to either commit the redo log changes made from the last time the virtual machine ran, discard the redo log, continue appending changes to the redo log or cancel the power on. The amount of space required by a redo log varies with the amount of information that has changed in the guest operating system and the frequency with which you commit changes. The longer the time between commitments of the redo log, the larger it grows. The redo-log file is placed in the same folder (directory) as the disk file by default. However, you can change the location of the redo-log file in the Configuration Editor. On a Windows host, click the Options tab, then type in or browse to the folder in which the redo log should be stored.
On a Linux host, click Misc on the left side of the Configuration Editor, then type in or choose the directory in which the redo log should be stored.
Changes to disks in nonpersistent mode are not saved to the disks, but are lost when the virtual machine is powered off or reset. Nonpersistent mode is convenient for people who always want to start with a virtual machine in the same state. Example uses include providing known environments for software test and technical support users as well as doing demonstrations of software. Any disk type can be used in nonpersistent mode. If your virtual disks are in nonpersistent mode, you can take advantage of the repeatable resume feature, which allows you to save the current state of the virtual machine when you suspend it, then resume from the point at which you suspended it every time you start the virtual machine. For more information, see Resuming Virtual Machines Repeatedly from the Same Point. GSX Server only reads the virtual disk file. Any writes to the virtual disk are actually written to a redo-log file. While you are running the virtual machine, any blocks that have been modified and written to the redo-log file are read from the redo-log file instead of the disk files. The redo-log file is deleted when you power off or reset the virtual machine. This is similar to the redo-log files used with disks in undoable mode. The redo-log file is placed by default in the folder defined by the host operating system's temp directory. However, the location of the redo-log file can be changed in the Configuration Editor. On a Windows host, click the Options tab, then type in or browse to the folder in which the redo log should be stored.
On a Linux host, click Misc on the left side of the Configuration Editor, then type in or choose the directory in which the redo log should be stored.
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