EMC – Broken Vault drive munts FAST Cache

Mat sent me an e-mail this morning, asking “why would FAST Cache be degraded after losing B0 E0 D2 in one of the CX4-960s?”. For those of you playing at home 0_0_2 is one of the Vault disks in the CX4 and VNX. Here’s a picture of the error:

Check out the 0x7576 that pops up shortly after the array says there’s a faulted disk. Here’s a closeup of the error:

Weird, huh?  So here’s the output of the naviseccli command that will give you the same information, but with a text-only feel.

"c:/Program Files/EMC/Navisphere CLI/NaviSECCli.exe"  -user Ebert -scope 0 -password xx -h 255.255.255.255  cache -fast -info -disks -status
Disks:
Bus 0 Enclosure 7 Disk 0
Bus 2 Enclosure 7 Disk 0
Bus 0 Enclosure 7 Disk 1
Bus 2 Enclosure 7 Disk 1
Bus 1 Enclosure 7 Disk 1
Bus 1 Enclosure 7 Disk 0
Bus 3 Enclosure 7 Disk 1
Bus 3 Enclosure 7 Disk 0
Mode:  Read/Write
Raid Type:  r_1
Size (GB):  366
State:  Enabled_Degraded
Current Operation:  N/A
Current Operation Status:  N/A
Current Operation Percent Completed:  N/A

So what’s with the degraded cache? The reason for this is that FAST Cache stores a small database on the first 3 drives (0_0_0, 0_0_1, 0_0_2). if any of these disks fail, FAST Cache flushes to disk and goes into a degraded state. But it shouldn’t, because the database is triple-mirrored. And what does it mean exactly? It means your FAST Cache is not processing writes at the moment. Which is considered “bad darts”.

This is a bug. Have a look on Powerlink for emc267579. Hopefully this will be fixed in R32 for the VNX. I couldn’t see details about the CX4 though. I strongly recommend that if you’re a CX4 user and you experience this issue, you raise a service request with your local EMC support mechanisms as soon as possible. The only way they get to know the severity of a problem is if people in the field feedback issues.