High I/O wait to NFS share on NAS

Solution Verified - Updated -


  • Our RHEL server runs processes to generate files. The files are stored on a NAS accessed over NFS.
  • Our server serves these files to a client via vsftpd. The speed of the FTP jobs has dropped from 60~70Mbps to ~160kbps.
  • We have observed high IO wait and FTP processes in D state for some time.
  • Remounting the NFS share results in all clients dropping out and failing, but high speed returns for a short time time.


  • Red Hat Enterprise Linux 5
  • RHEL system is NFS client to a NAS filer
  • RHEL system is FTP server to external FTP clients

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