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FWBC on Proliant DL380 G8 - P420i

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visna77
Occasional Advisor

FWBC on Proliant DL380 G8 - P420i

Hello guys,

I've some DL380p G8 with P420i/1Gb  (709942-421), I don't know why write back cache is always disable though battery is ok and charged. 

So I 've a doubt if I can enable FWBC or not, because I don't want risk lose data.

 

In old Proliant FWBC was enable when battery was charged.

 

Someone can explain this? What is your advices?

 

thanks

Andrew

7 REPLIES
waaronb
Respected Contributor

Re: FWBC on Proliant DL380 G8 - P420i

Does the array config actually show the battery (super cap in this case) is actually fully charged?

There's a firmware update for the P420s that fixed a problem where it would report the super-cap as still charging even though it was fully charged. We had that issue on one of our servers and the firmware update fixed it.

If the config util is showing the battery is fully charged and the write cache is still being force-disabled, that sounds like some other issue, but I'd start out by making sure the latest firmware is installed on the controller (version 5.42).
visna77
Occasional Advisor

Re: FWBC on Proliant DL380 G8 - P420i

In vmware client there is  a info on Battery and it shows Full Charged.  Same info is in  ACU utility also.

Firmware is just upgraded to 5.42.

 

So I can enable FWBC on server but my doubt is:  if powerless event occurs and server is not under UPS protection (or UPS does not works fine and poweroff server without correct sequence), what can I risk if super-cap is fully charged?

 

Which benefit (in percentage) I can give with FWBC enabled versus disabled?

 

Thanks again

Andrea

waaronb
Respected Contributor

Re: FWBC on Proliant DL380 G8 - P420i

With a flash-backed cache, the cache is using flash memory to backup any data in the RAM cache itself during a power outage.

The way it works, there's a RAM cache (nice and fast) during normal use... it makes a big difference for write caching which is why the default is 80% write/20% read.

If there's a power outage, the super-cap has enough power to be able to copy the contents of the RAM cache into flash memory. It happens pretty quick.

When power is restored and the machine starts up, any unwritten data in the flash cache is written to disk.

This is a much better solution than the old battery backed cache... with that, there are some batteries that supply power to the RAM cache itself. I think they say there's enough power to keep the memory alive for 3 days, but if your power outage lasts longer than that, it's gone. With the flash cache, it doesn't matter how long the outage lasts, it'll be there in NVRAM indefinitely.

Plus, the supercaps tend to last longer than lithium or nicad batteries and recharge quicker. All in all it's a better and safer solution.

Hope that helps answer your question about the safety and reliability of FBWC.
visna77
Occasional Advisor

Re: FWBC on Proliant DL380 G8 - P420i

thanks, you have explained very well !

 

So I can enable FWBC safety, and then I can see which real benefits I can get whit it.

 

 

 

 

 

visna77
Occasional Advisor

Re: FWBC on Proliant DL380 G8 - P420i

Hello, sorry but how I can find if FBWC is enabled on DL380p G8?

 

I've enter on Smart Array Bios Config and  there is only this option that is disabled:

 

"Enable write cache battery override" 

 

Is it?  Or I have to enable from Intelligent Provisioning?


Thanks very much

Andrea

 

 

 

 

waaronb
Respected Contributor
Solution

Re: FWBC on Proliant DL380 G8 - P420i

When it's booting up, select the option to use the full GUI array config program (sorry, I don't remember the exact key to press). It's different than the usual F8 to enter the more limited configuration program.

The full GUI option is similar to the SSA program in Windows or from the SPP DVD and allows you to configure advanced array options, cache settings, etc. That's new to the Gen8 models and P420 controllers.

I'd look right now to see exactly how to enter that, but all my Gen8 boxes are production so I can't reboot one to check. :)

The write cache should be enabled by default though, with 80% write and 20% read.

There's an additional option that lets you enable the write-through cache on the physical drives themselves. That one is disabled by default and should only be enabled if the server has some kind of UPS to make sure it doesn't lose power unexpectedly.

That option turns on the drive's built in write-caching, using whatever memory the drive itself has. Since the controller is doing write-caching of it's own and that one *is* battery backed, I'd recommend leaving the drive's native cache disabled since it won't add that much value while adding more risk.
visna77
Occasional Advisor

Re: FWBC on Proliant DL380 G8 - P420i

Now I understand it  :)

 so Write cache on my server is already enebled and I set ratio 70% write and 30% read.

The other option write-through cache I leave it disable.

 

Thanks very much