On Tue, Sep 13, 2011 at 2:11 AM, Oper.ML 
<oper.ml@xxxxxxxxx> wrote:
  
    
  
  
    Hi guys,
      
          i have 4 debian squeeze with xen 4 and all them with 4 to 6
      HVM virtual machines. All the VMs are located in a fith machine (A
      SuperMicro LSI Controller as storage).
          The host servers are Intel i7 with 24GB fo RAM (Debian Squeeze
      + Xen4) and the storage a Xen 3.0 with 8GB of RAM (CentOS 5.5 +
      TGTD) and thery are all connect with a
      gigabit network dedicated for the iSCSI.
          My problem is, when working at the storage, doing backup
      procedures with the command dd and using the bzip2, the IOWait
      increases a litle bit, the normal state is close to 0%, but when
      copying or moving the files generated by the backup, usually
      bigger than 2G, the IOWait increases too much, reaching 100%, in
      cases in all 4 cores, making the virtual machines stop responding
      and even if i stop the procedure, the virtual machines doesnt
      comes back, been necessary a reboot or shutdown.
          Does anyone knows about this problem ? And there is any
      configuration that i could do in the iSCSI-Target and Initiator to
      increase de performance? And a configuration in the virtual
      machines filesystem to prevent it from stopping?
      
      Thanks you all,
      Regards,
      Tny M.
    
  
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What is the specs of your storage server?
It sounds like the storage server is underpowered or overloaded quite a lot.