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    SubjectRe: [PATCH 26/30] ext4: do not send discards as barriers
    Boaz Harrosh, on 08/31/2010 01:55 PM wrote:
    >>>>>> An update: I've set up an ext4 barrier testing in KVM - run fsstress,
    >>>>>> kill KVM at some random moment and check that the filesystem is consistent
    >>>>>> (kvm is run in cache=writeback mode to simulate disk cache). About 70 runs
    >>>>>
    >>>>> But doesn't your "disk cache" survive the "power cycle" of your guest?
    >>>> Yes, you're right. Thinking about it now the test setup was wrong because
    >>>> it didn't refuse writes to the VM's data partition after the moment I
    >>>> killed KVM. Thanks for catching this. I will probably have to use the fault
    >>>> injection on the host to disallow writing the device at a certain moment.
    >>>> Or does somebody have a better option?
    >>>
    >>> Have you considered to setup a second box as an iSCSI target (e.g.
    >>> with iSCSI-SCST)? With it killing the connectivity is just a matter
    >>> of a single iptables command + a lot more options.
    >
    > Still same problem no? the data is still cached on the backing store device
    > how do you trash the cached data?

    If you need to kill the device's cache you can crash/panic/power off the
    target. That also can be well scriptable.

    Vlad


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