Crawl fails to index data and doesn't show any update in crawl log
I observed this issue recently for a SharePoint\Fast Search for SharePoint 2010 farm set up. Crawl was going into a infinite state without any errors and updates. There were no indication in crawl log for any success or failures. It was all working fine and there was no change to system\farm setup.
I tried verifying SharePoint\Fast services, everything seems to be working fine. Therefore, I tried accessing the default search url (https://localhost:13280) in FAST and performed a simple search. The search resulted in an error with description "All partitions are down Code: 1003". On looking further in eventlog found the error "We are low on disk space, waiting for disk space to be freed".
It turned out to be the disk space issue.The fast installation drive was having much lower disk space than the recommended one.