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Lustre 1.6 Operations Manual

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Why can't I run an OST and a client on the same machine?<br />

Consider the case of a "client" with dirty filesystem pages in memory and memory<br />

pressure. A kernel thread is woken to flush dirty pages to the filesystem, and it<br />

writes to local OST. The OST needs to do an allocation in order to complete the<br />

write. The allocation is blocked, waiting for the above kernel thread to complete the<br />

write and free up some memory. This is a deadlock.<br />

Also, if the node with both a client and OST crash, then the OST waits, during<br />

recovery, for the client that was mounted on that node to recover. However, since the<br />

client crashed, it is considered a new client to the OST, and is blocked from<br />

mounting until recovery completes. As a result, this is currently considered a double<br />

failure and recovery cannot complete successfully.<br />

Appendix D <strong>Lustre</strong> Knowledge Base D-27

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