Avamar: How to enable the demand-paging cache introduced in Avamar 7

From Avamar 7 and later, a new client cache format has been introduced called demand-paging cache. The demand-paging cache loads parts of the cache to RAM depending on the directory the backup being processed. This minimizes RAM requirements. The new cache automatically adjusts its size in relation to the type and amount of data on the client.

This article describes how to leverage the demand-paging cache in Avamar 7. The feature may help in some of the following circumstances.

• Backup data is sent to Data Domain.
• The client dataset contains millions of files.
• Backups are consuming a lot of RAM on the client.
• It is not possible to resize the size cache due to insufficient RAM on the client.
• The backup dataset contains directories with millions of files in them.
• Backups do not finish within the backup window.
• Backups finish within the backup window but are running slow.

The monolithic client cache files f_cache.dat and p_cache.dat are loaded entirely into the client's RAM.  

These caches are large on clients with lots of data or millions of files. Where clients lack enough RAM, cache tuning is required.

The demand-paging cache requires 10 to 20 times more disk space compared with the traditional cache.  

To prevent clients from running out of disk space, it is not used by default.

Space required by the paging cache

The cache needs 1 GB per 10 million of files on the client * the number of consecutive backups (up to 16) which are stored in the client cache.

Calculate the approximate size of the demand-paging file using the following formula:

 (# of millions of files)/10 * 1 GB * 16 = (# of GB required for demand-paging file cache)

If the client does not have enough space on the disk, it is recommended that the client continues to use the monolithic cache if possible. Avamar client software can also be reinstalled to another drive with more space.

In order to enable the demand-paging cache, the client must be running Avamar client 7.0.0 or later.

Enabling the paging cache on a dataset

All the clients using the modified dataset must be running Avamar client 7.0.0 or later and have the necessary disk space to hold the demand-paging cache. Clients on a lower version fail the backup. Clients with insufficient space should not be configured to use the paging cache.

1. In Avamar Administrator, select Tools > Manage Datasets
2. Go to the dataset that you would like to change and select Edit.
3. Select Options tab and click More options.
4. Under the Item type:  [avtar]paging-cache
5. Under Value type:  True
6. Select the '+' sign to apply the switch.

Enabling the paging cache on a single client

1. Log in to the client  
2. Go to the installation var directory (Default: C:/Program Files/avs/var)
3. Create a file called avtar.cmd, if not present.
4. Edit the file and put the following on a new line:  

5. Save the file.

Note: The new configuration takes effect during the next scheduled backup. The transition period from one cache type to another is 14 days. During that time, the client uses both caches. Expect no change in backup performance yet. After the transition period, only the demand-paging cache will be used. This should result in improved backup performance for large clients. The old cache file will be automatically removed after 180 days.

For more information about the new paging cache file, see Page 52 of the "Operational Best Practices" guide for Avamar 7:
https://support.emc.com/docu48217_Avamar-7.0-Operational-Best-Practices.pdf?language=en_US