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We have just discovered that a large buffer cache generated from traversing a lustre file system will cause a significant system overhead for applications with high memory demands. We have seen a 50% slowdown or worse for applications. Even High Performance Linpack, that have no file IO whatsoever is affected. The only remedy seems to be to empty the buffer cache from memory by running

I'd like to know what the cause of a particular DB server's slowdown might be. We've ruled out IOPs for the disks (~ 20%) and raw CPU load (top shows perhaps 1/2 of cores busy, but the system slows to a crawl. We're suspecting that we're simply running out of memory bandwidth but have no way to confirm this suspicion. Is there a way to test for this? Think: iostat but for