Monday, March 2, 2009

Question of the week : Storage DS On/Off Command

Question of the week:

I’ve Can you verify there is no way to power down the SAN controllers? I have a customer looking to script shutdown sequences in case the UPS runs low on power, is it possible to do anything beyond powering off the hosts and flushing caches?

Answer of the week:

Yes, I will verify that there is no “power down” command for the DS3000/DS4000/DS5000 series storage arrays except for the physical switch on the power supply.

The engineering team has argued both for and against this feature for a long time. I, in fact, argued for a long time for the inclusion of a power-down command, but generally tend to agree with the engineering stance against it (which means they’ll probably add the capability someday)

The “downside” of having this seems to outweigh the convenience of having the feature. Downside being the unwanted result of someone accidently, or maliciously, executing a command which remotely turns off the SAN storage.

For the power-down situation mentioned above, the system is well prepared. Unlike our competitors, our system will automatically flush the write cache to disk after 10 seconds of inactivity (adjustable on a LUN-by-LUN basis). This means there are no worries from the storage side. As long as the servers are shut down in an orderly manner; applications are exited and the servers are shut down. The memory will be flushed to the storage array, and the storage array will push everything to disk. This is exactly the desired sequence and state of the machines for a controlled power-down. All data is consistent, and a smooth startup will occur.

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