Tag Archives: Promise Pegasus2 hackery

Sometimes, you stumble on the right person…

…and they reveal to you a bit of magic you didn’t know existed.

In this case, it is an undocumented flag in Promise Technology’s command line utility for the Promise Pegasus2 Thunderbolt RAID, promiseutil.

As previously discussed, it appeared to be impossible to check the status of more than one Promise Pegasus enclosure from inside a script using promiseutil. We had filed a support ticket, hoping for some kind of resolution, but were told that promiseutil works as intended.

On a hunch, I reached out to someone at Promise and asked for their help investigating this issue.  I was pleasantly surprised when the contact not only took the issue seriously, he immediately looped in other support engineers to look at the problem.

After a week of back and forth about what an appropriate solution would be, perhaps a feature request, the support engineer discovered that there is an undocumented flag that allows you to specify the hba of the Promise unit you want to execute a command on.

Here’s an example. Let’s say we want to check the SMART status of two Promise Pegasus from the command line:

 promiseutil -C smart -v

will return the information for the default device only.

If you want to be explicit about which Promise Pegasus you’re checking, first get the hba numbers of the connected units:

promiseutil -C spath

The results will be something like this:

archer:~ admin$ promiseutil -C spath
Type  #    Model        Alias   WWN          Seq
hba   1  * Pegasus2 R4       2000-0001-5558-2fe2  1
hba   2    Pegasus2 M4       2000-0001-5558-3f92  1

Now we use the magic (apparently undocumented) -P (uppercase, not the documented lowercase) flag to specify the unit we want to look at.

promiseutil -T hba -P 1 -C smart -v

which returns the results for the first unit.

promiseutil -T hba -P 2 -C smart -v

will return results for the second unit.

My sincere thanks to the people at Promise who helped us sort this out (you know who you are) and to my fellow bug wrestler, Allen Hancock of Watchman Monitoring.

As always, be cautious with promiseutil. Its power is mighty and Bad Things® can happen if used incorrectly.

Scanning more than one Promise device with promiseutil

So, comes the day when you have more than a single Promise Pegasus attached to a Mac and you’d like to leverage some of your utilities to check the second device.

“No problem,” you think, “I’ll just count the number of devices, then check each one in sequence.”


promiseutil is broken in one, very important way.

From inside promiseutil, the command to switch to the second unit in the chain would be something like:

spath -a chgpath -t hba -p 2

And that command works just fine. But as we’ve seen from previous work, executing promiseutil from inside a bash script requires the use of the screen command.

Executing this command from inside promiseutil run under screen does not work correctly. promiseutil appears to ignore the command and remains on the default device.

The official response from Promise is as follows:

This has been made/designed in a way to work as it is described in the KB article (and it is not a bug,but that’s how it has been designed to work) that was given on my earlier reply and it can’t used in the way that you have given and I am sorry that there are no work around available.

If you know someone at Promise and have any influence, it would be a significant improvement to have this bug removed from the next release of the promiseutil.

Heck, if you’re feeling bored, file a bug report with them here.