Poor write performance on Debian server running NFS with 22TB exported JFS filesystem

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http://serverfault.com – I am currently running a debian server that is exporting a large JFS filesystem (22TB) over NFS (nfs-kernel-server.) When attempting to write to the NFS share, the performance is very poor. The 22TB disk is sitting on a NAS mounted using iSCSI. It will bust for a moment near expected line speed, and then sit idle for several seconds. Very little traffic measured in the low kb/sec. The wait peeks on write. When reading from the NFS mount, the system operates at expected speeds (11MB/sec). The issue does not occur when using SFTP, rsync, or local coping (non-nfs). The issue persists betw (HowTos)