We've seen a few instances of leveldb failing on compaction as it is missing an SST file
2012/06/12-20:23:41.713048 97 Generated table #422226: 563 keys, 2107848 bytes
88026049394855470996013819413191996189691609088/107719.sst: No such file or directory
Possible theory is the file being added to the MANIFEST before actually being created on disk and then having problems during creation.
Issue found / resolved. Riak was able to reopen a vnode before its close operation completed. Took three passes at "fixing" the leveldb locking stuff ... but seems to be addressed.