HP Storage Mirroring V5 Software - Manual (Page 113)

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4. Specify the Maximum system memory for queue . This is the amount of Windows system memory, in MB, that will be
used to store data in queues. When exceeded, queuing to disk will be triggered. This value is dependent on the amount
of physical memory available but has a minimum of 32 MB. By default, 128 or 512 MB of memory is used, depending on
your operating system. If you set it lower, Storage Mirroring will use less system memory, but you will queue to disk
sooner which may impact system performance. If you set it higher, Storage Mirroring will maximize system performance
by not queuing to disk as soon, but the system may have to swap the memory to disk if the system memory is not
available.
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 SQL Server will 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 SQL Server. 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
SQL Server and Storage Mirroring, you might configure SQL Server 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 service 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 Windows Event Viewer. 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.