IBM CMOD Cache Filesystems

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IBM Content Manager OnDemand Cache Filesystem

Here are some frequently asked questions about the IBM CMOD cache.

What is the IBM CMOD Cache filesystem?

The CMOD cache filesystem, often named “arscache” is a pool of storage on your IBM CMOD server that Content Manager OnDemand uses to store documents for fast loading or retrieval. IBM CMOD Application Groups are configured by default to load data into the cache filesystem, and migrate it to secondary storage at a later time. Migrating the data from the CMOD cache to secondary storage doesn’t delete it - the caches are kept at 80% by default, to help make retrievals for end users faster. One of the easiest ways to tune the OnDemand Cache performance on large Content Manager OnDemand installations is to increase this number to over 95%.

Where do I configure the behavior of the CMOD cache?

Inside the Content Manager OnDemand Administrator Client, in the Application Group window, on the Storage Management tab, there’s a button labelled ‘Advanced’ that will allow you to change how Application Group data is managed.

Diagram: Configuring IBM CMOD Cache behavior

CacheConfiguration.png

How does the cache get filled?

As you load data into IBM Content Manager OnDemand, data is placed into the caches for fast access. The only exception to this rule is if you choose not to load Application Group data to the cache at all, and send them directly to secondary storage - which is generally reserved for situations where documents need to be archived for legal or regulatory reasons, but are rarely, if ever, accessed.

If you have more than one cache filesytem, IBM CMOD chooses the cache with the most free space, and puts the compressed objects generated by the load there.

How does the cache get emptied?

You can reduce the amount of data in the cache filesystems with the arsmaint command. You will want to migrate any data with the arsmaint -m command first, then run the arsmaint -c command to delete eligible items from the cache. You can combine both options in the same command (arsmaint -mc ) to perform both tasks.

What is cache expiration?

CMOD Cache expiration is the process by which OnDemand reduces the amount of data inside the caches, in order to make room for new data that is loaded into your Content Manager OnDemand server. It does this by removing data that has already been migrated to secondary storage or is eligible for expiration, starting with the oldest documents first, until the filesystems are approximately 80% full by default. As mentioned above, on large IBM CMOD servers that have multiple terabytes of cache, adjusting the minimum and maximum parameters makes optimal use of your expensive cache filesystems. You can visit the arsmaint page to find out more about how you can clear data from the IBM CMOD cache filesystem.

What is cache optimization?

Storage is expensive and finite. In order to make the most out of the storage space you have in your IBM CMOD Cache filesystems, you should try to store more of the data that users are actually accessing, for the period of time that they’re interested in them. You can optimize the cache contents so that you’re using precisely enough disk to perform the required retrievals and to have enough space to load new data. An optimized cache contains only the data people are accessing. Unfortunately, there's no built-in tool for performing the Content Manager OnDemand Cache.

How can I optimize the IBM CMOD Cache?

If your IBM CMOD Cache Filesystems are large (over 1 terbyte) then the default setting for the arsmaint -c will leave 20% - 200 gigabytes of empty cache. If you have multiple 1TB cache filesytems, and you only load 20GB per day, you could have a huge amount of wasted space in your caches. You can adjust this number with the -m and -n options for arsmaint to set new maximum and minimum caches sizes during cache expiration.

The other ways to tune the cache filesystems are to analyse the patterns of retrievals of Application Group data, and change the cache retention to match actual end user usage, and to use data from your load and retrieval patterns to determine your optimal cache size. If you need help optimizing your cache filesystem, visit CMOD Cloud’s Cache Optimization page.

Can I delete files in the cache manually?

NO! The cache is only to be managed withthe arsmaint utility to reduce the amount of data stored in your cache filesystems, and make space for new documents in the cache.

Too late, I already deleted files from my CMOD cache filesystem. Help!

If you have a backup of your cache data in your enterprise backup system, you can probably recover the missing data. You can contact Tenacious Consulting for assistance. They have tools to help you restore and verify the contents of your cache, or to pull data from secondary storage back into the CMOD cache.

What are the retr and migr directories?

Someone’s been spelunking! The retr and migr directories inside the cache help CMOD retrieve and migrate documents. There’s a very good presentation on the OnDemand User’s Group forums on the cache filesystem internals. Registration on the forums is required to access the presentation - and new registrations are normally approved within 48 hours.

How do I add more cache filesystems?

Simply add an entry to the CMOD ars.cache configuration file. If you have more than one Content Manager OnDemand instance configured on your IBM CMOD server, then you’ll need to edit the file specified by SRVR_SM_CONFIG in the instance definition in your ars.ini configuration file.

Can I remove a cache filesystem?

Yes, and no. You can remove a filesystem from the ars.cache configuration file, and CMOD will stop adding data to it during loads, and will expire data from it during cache expiration processing. However, your IBM CMOD server will NOT redistribute objects to other caches. If you want to consolidate your existing caches into a smaller collection of caches, visit Cache Consolidation for assistance.

Can I balance the data in the cache filesystem?

Content Manager OnDemand automatically balances the amount of data in caches by placing new CMOD object files in the cache with the most free space, measured in blocks of free space in the filesystem. If you have a large number of cache filesystems with dramatically different utilization, see this article on Cache Consiolidation.

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