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My issue is that our company is running three physical servers, each running 4-5 virtual servers, and they are all pulling data from one qnap. My question is, I know it's possible to do real-time replication to set up a redundant qnap using rsync and rtss. However, I'm not certain whether or not these programs will replicate the iSCSI targets. If our primary qnap goes down, we'd like to be able to switch to the secondary one relatively quickly. Any answers to this issue will be greatly appreciated.

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up vote 3 down vote accepted

As far as I'm aware, you can't use these features (rsync and rtss) on iSCSI volumes. We recently went through the same investigation.

This is definately true on the lower-level QNAPs, such as the 419.

The reason is those protocols only work on a file-level, not a block-level.

There is however block-level replication in their high-end devices, but I haven't looked into it much as they were out of our clients budget.

The higher-level devices are (were, at least) cerfified for VMWare SRM, which requires block-level replication. Turns out I was confused. There's no block-level replication on QNAPs as far as I'm aware.

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Basically replication (especially synchronous replication) has to be done by the storage itself. For replication to happen, you need to have the information about which data has changed when. There is no way to tell this from a storage client's perspective.

There are Qnap models that do support replication using a common protocol - you would need two of those.

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