HP Storage Mirroring Software - Manual (Page 61)

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Since the source is typically running a production application, it is important that the amount of
memory Storage Mirroring and the other applications use does not exceed the amount of RAM in
the system. If the applications are configured to use more memory than there is RAM, the
system will begin to swap pages of memory to disk and the system performance will degrade.
For example, by default an application may be configured to use all of the available system
memory when needed, and this may happen during high-load operations. These high-load
operations cause Storage Mirroring to need memory to queue the data being changed by the
application. In this case, you would need to configure the applications so that they collectively do
not exceed the amount of RAM on the server. Perhaps on a server with 1 GB of RAM running the
application and Storage Mirroring, you might configure the application to use 512 MB and
Storage Mirroring to use 256 MB, leaving 256 MB for the operating system and other applications
on the system. Many server applications default to using all available system memory, so it is
important to check and configure applications appropriately, particularly on high-capacity
servers.
Any changes to the memory usage will not take effect until the Storage Mirroring daemon has
been restarted on the server.
5. Specify the Maximum disk space for queue. This is the maximum amount of disk space, in
MB, in the specified Folder that can be used for Storage Mirroring disk queuing, or you can select
Unlimited which will allow the queue usage to automatically expand whenever the available
disk space expands. When the disk space limit is reached, Storage Mirroring will automatically
begin the auto-disconnect process. By default, Storage Mirroring will use an unlimited amount of
disk space. Setting this value to zero (
0
) disables disk queuing.
6. Specify the Minimum Free Space. This is the minimum amount of disk space in the specified
Folder that must be available at all times. By default, 50 MB of disk space will always remain
free. The Minimum Free Space should be less than the amount of physical disk space minus
Maximum disk space for queue.
7. Specify the Alert at following queue usage percentage. This is the percentage of the disk
queue that must be in use to trigger an alert message in the Linux system log. By default, the
alert will be generated when the queue reaches 50%.
8. Click OK to save the settings.
NOTE: The Maximum disk space for queue and Minimum Free Space settings work in
conjunction with each other. For example, assume your queues are stored on a 10 GB
disk with the Maximum disk space for queue set to 10 GB and the Minimum Free
Space set to 500 MB. If another program uses 5 GB, Storage Mirroring will only be
able to use 4.5 GB so that 500 MB remains free.