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Lustre 1.6 Operations Manual

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33.12 OSS RAM Size for a Single OST<br />

For a single OST, there is no strict rule to size the OSS RAM. However, as a<br />

guideline, 1GB per OST is a reasonable RAM size. This provides sufficient RAM for<br />

the OS, and an appropriate amount (600 MB) for the metadata cache, which is very<br />

important for efficient object creation/lookup when there are many objects.<br />

The minimum, recommended RAM size is 600 MB per OST, plus 500 MB for the<br />

metadata cache. In a failover scenario, you should double these sizes (therefore 1.2<br />

GB per OST).<br />

In this case, you have about 1.2GB/OST. It might be difficult to work with<br />

1GB/primary OST as it gives 800MB/2OST which leaves only 100MB for a working<br />

set for each OST. This ends up as a maximum of ~ 2.4 million objects on the OST<br />

before it starts getting thrashed.<br />

Chapter 33 System Limits 33-5

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