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 between stable and testing releases. On the same machine I have a 14TB ext4 filesystem using the exact same export configuration that does not share the issue. This share is not in regular use and thus not consuming resources. NFS Server: cat /etc/exports /data2 10.1.20.86(rw,no_subtree_check,async,all_squash) cat /sys/block/sdb/queue/scheduler noop [deadline] cfq cat /etc/default/nfs-kernel-server RPCNFSDCOUNT=8 RPCNFSDPRIORITY=0 RPCMOUNTDOPTS=--manage-gids NEED_SVCGSSD= RPCSVCGSSDOPTS= NFS Client: cat /etc/fstab 10.1.20.100:/data2 /root/incoming nfs rw,noatime,soft,intr,noacl 0 2 cat /sys/block/sdb/queue/scheduler noop [deadline] cfq cat /proc/mounts 10.1.20.100:/data2/ /root/incoming nfs4 rw,noatime,vers=4,rsize=262144,wsize=262144,namlen=255,soft,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=10.1.20.86,minorversion=0,addr=10.1.20.100 0 0 This problem has me pretty stumped. Any help would be greatly welcomed. Thanks.