I had a reader email me with a few questions about Dell’s PowerEdge VRTX 2nd PERC, so I thought I’d write about it with the intent on helping others.  If you have other blade-related questions (whether Dell or not) let me know and I’ll see what I can find.

I have a few questions about the (2nd) PERC controllers (on the VRTX) now that WB (write-back) is supported in a dual controller configuration and was wondering if you can help:
1. Are the PERCs still active/passive?
2. How are the caches on each card kept consistent?
3. Do the PERCs have have battery backup?
a. If so, how often do the batteries need replacing?
b. Do I need to power off the VRTX chassis to perform this replacement?
c. if the battery failed then the cards go into write through mode, is this correct?

These are all great questions that I had to go to the Dell product manager to find out.  To be completely transparent, I received an answer to these questions fairly quickly, but I’ve been procrastinating publishing this but here are the answers that were provided in regards to Dell’s 2nd Shared PowerEdge RAID Controller on the VRTX:

1. Are the PERCs (PowerEdge RAID Controllers) still active/passive?
Answer: yes

2. How are the caches on each card kept consistent?
Answer: In write-back mode, an IO does not complete back to the host until the cache on both controllers have been updated.

3. Do the PERCs have have battery backup?
Answer: yes

a. If so, how often do the batteries need replacing?
Answer: Batteries for Dell’s PowerEdge RAID Controller (PERC) have a 3-year warranty.

b. Do I need to power off the VRTX chassis to perform this replacement?
If the user already has 2 PowerEdge VRTX Shared PERCs, then the blades must be all powered down first.  Dell has the update procedures in the Dell PowerEdge VRTX Storage Subsystem Compatibility Matrix here:  http://www.dell.com/support/home/us/en/19/product-support/product/poweredge-vrtx/manuals   

c. if the battery failed then the cards go into write through mode, is this correct?
If the battery on the active controller dies, then yes the VDs (virtual disks) will transition to WT (write-through).  If the battery on the passive controller dies, then the VDs will not transition to WT unless/until a failover occurs and the passive controller becomes active.   One note:  There is a case where if the passive battery dies, the VDs on the active may go to WT, but after a controller reset (i.e., chassis power cycle) the VDs will transition back to WB, as long the battery remains good on the active.

Thanks to the reader for submitting this question – I hope this helps you and many others looking or using the Dell PowerEdge VRTX.  As mentioned above, if you have other blade server related questions, for ANY vendor – please let me know and I’ll see what I can find.  Thanks for reading!
Kevin Houston is the founder and Editor-in-Chief of BladesMadeSimple.com.  He has over 17 years of experience in the x86 server marketplace.  Since 1997 Kevin has worked at several resellers in the Atlanta area, and has a vast array of competitive x86 server knowledge and certifications as well as an in-depth understanding of VMware and Citrix virtualization.  Kevin works for Dell as a Server Sales Engineer covering the Global Enterprise market.