PowerFlex 3.0: "Device media type mismatch" alert when adding a new device to SDS

 - New install of VxFlex OS 3.0
 - Adding new devices to an SDS
 - Alert will also show when changing the the media type of pool to differ from the device media type.

Symptoms

 - When adding a new device to a pool with media type set to SSD, the following messages show in the MDM events:
 

2019-04-02 16:19:23.517 SDS_DEV_MEDIA_TYPE_MISMATCH WARNING  	 Performance metrics on SDS 00007f54d652e460 device /dev/sdb indicate a media type mismatch. Expected SSD, detected HDD. Check the health of mismatched device, or replace the device. 
2019-04-02 16:19:24.528 SDS_DEV_MEDIA_TYPE_MISMATCH WARNING  	 Performance metrics on SDS 00007f54d6537460 device /dev/sdc indicate a media type mismatch. Expected SSD, detected HDD. Check the health of mismatched device, or replace the device.

The following alert will show in the GUI "Alerts" tab:
 
The SDS trc logs show the following when adding the device:

02/04 16:18:56.973216 0x7f4ca2961db8:file_DeviceTypeTest_Run:00400: Device type test [devId df77712b00020000 /dev/sdb]: starting test in bound UMT [try 1 max 2]
02/04 16:18:59.835296 0x7f4ca57cfdb8:file_DeviceTypeTest_RunTest:00335: Device type test [devId df77712b00020000 /dev/sdb]: test summary: detected type DATA_SPINDLE, 
test time 2861989 micros, total IOs 128, fast IOs percentage 0, --- test thresholds: time spindle >= 256000 flash <= 64000, fast IOs percentage flash >= 80
02/04 16:19:01.353528 0x7f4ca2961db8:file_DeviceTypeTest_Run:00400: Device type test [devId df77712b00020000 /dev/sdb]: starting test in bound UMT [try 2 max 2]
02/04 16:19:11.744518 0x7f4ca435bdb8:file_DeviceTypeTest_RunTest:00335: Device type test [devId df77712b00020000 /dev/sdb]: test summary: detected type DATA_SPINDLE, 
test time 10390761 micros, total IOs 512, fast IOs percentage 0, --- test thresholds: time spindle >= 1024000 flash <= 256000, fast IOs percentage flash >= 80
02/04 16:19:11.744587 0x7f4ca2961db8:file_DeviceTypeTest_Run:00415: Device type test [devId df77712b00020000 /dev/sdb]: ended test [try 2 max 2] detected DATA_SPINDLE expected DATA_FLASH

Impact

If the device is being added to a Fine granularity (FG) pool, the device is added but be marked as errored and not usable. 

If the device is being added to an MG pool, the device adds and the alert will stay in the UI.

Root Cause

In VxFlex OS 3.0, designating a media type for pools and disks was introduced for various reasons, one of them being that only SSDs can be added to an FG Fine Granularity pool. When adding a new disk to an SDS, the SDS tests the disk to make sure it passes the performance metrics designed to identify an SSD. 

The test has two metrics:
 - overall execution time of all IOs sent to the disk. The IOs are sent in parallel to random offsets in the disk.
 - percentage of "fast IOs" as indicated by the time expected to return for those IOs must be > 80%.

If the disk fails the first test, the SDS runs the test again with more IOs to make sure the first test was not a fluke. As noted in the trc output from above, the total time taken in the second test, which sent 512 IOs, was over 10 s. Furthermore, none of the IOs returned under the time thresholds necessary to mark them as "fast IOs." Thus this disk was marked as a hard drive in an SSD media type pool.

The first thing to do here is remove and re-add the disk. 

If the disk continues to show performance metrics that do not match the disk type and the alert returns, the hardware side must be checked. Verify the controller and driver are set up properly and run disk speed tests as needed. Involve the hardware vendor as necessary.

Impacted Versions

VxFlex OS 3.0 and above

Fixed In Version

This is a hardware issue.