[ubuntu] Why is tar so slow at writing to a cifs share?

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http://ubuntuforums.org – This is on Ubuntu 10.04. I can write to my cifs share at 250 mbps with cp. I can tar over my nfs network at close to gigabit speed. But when I tar to my cifs share, I am only getting 70 mbps. Any idea how this can happen? Here is my mount command from /etc/fstab: //zzz-address /zzz-mount-location cifs credentials=/root/smb/credentials.mbb,uid=0,gid=0 0 0 And here is the tar command: tar --listed-incremental zzz.snar -cpPf zzz.tar Any help would be greatly appreciated! Thanks. (Hardware)