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Re: [dm-devel] [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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