Article ID: 126085, created on Jul 5, 2015, last review on Jun 17, 2016

  • Applies to:
  • Virtuozzo 6.0


iSCSI targets are slow inside of the VM. e.g. direct write speed on Virtuozzo node connected to Virtuozzo storage is 200 MB/s, while inside VM write speed to Virtuozzo storage via iSCSI can be several time slower (20MB/s)


It is expected behavior that iSCSI clients would have slower communication with Virtuozzo storage than native pstorage-mount clients, as pstorage-iscsi service works on top of pstorage-mount service.

There are 3 points to check for performance degradation:

  1. Virtuozzo storage performance,

  2. Load average and memory usage on the client Virtuozzo node,

  3. A performance issues on initiator (VM) level.


While it does not make much sense to use iSCSI disks in virtual machines on Virtuozzo nodes(VM's harddisk images should be placed in natively mounted cluster folder), it was found that the following performance issues can be addressed in virtual machines to improve iSCSI performance:

  • More advanced NIC driver emulation mode should be selected, e.g, in Virtuozzo virtio network driver provide better performance rather then e1000 or rtl

    to change NIC type of VM to virtio:

    # prlctl set VMNAME --device-set net0 --adapter-type virtio

NOTE: Virtual Machine restart is required after changing the adapter type.

  • Virtual Machine's CPU spends a lot of time by service hardware and software interrupts. This can be checked with top utility(%hi and %si counters) while I\O load testing.

    irqbalance service can be used for performance improvement in VM:

    # yum install irqbalance
    # service irqbalance start

The considerations above should be taken into account when troubleshooting pstorage-iSCSI performance issues with 3rd-party virtualization solutions or hardware servers.

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