topic P4500G2 cache 100% Read / 0% write in StoreVirtual Storage

P4500G2 cache 100% Read / 0% write

derlendson — Mon, 31 Aug 2015 17:35:54 GMT

Hello all,

We recently replaced the BBU Cache on all six nodes in our P4500G2 due to two of the six failing (age it is assumed). Prior to replacing the BBU Cache we had acceptable performance on our LeftHand and I am confident that all six of the nodes reported a cache ratio of 50% / 50%.

After the BBU Cache replacement all six nodes are now showing 100% read / 0% write and our performance is abysmal. Any ideas on why the Cache Ratio changed, and more importantly how do I change it back? We still have support on the nodes, should I contact HP on this?

If it's an easy change I'll just get it done, however I'm not seeing anything in the CMC and my 'google-fu' isn't returning any appropriate results.

Thanks!

Re: P4500G2 cache 100% Read / 0% write

Dennis Handly — Tue, 01 Sep 2015 06:26:33 GMT

>After the BBU Cache replacement all six nodes are now showing 100% read / 0% write and our performance is abysmal.

That's expected. What is the charge on your BBU?

I'm not sure if it will automatically change to a better value once 100% charged?

Re: P4500G2 cache 100% Read / 0% write

derlendson — Tue, 01 Sep 2015 16:37:18 GMT

Hi and thanks for the reply,

Here is the screen info from the diagnostics page:

    Cache Status   Normal
    Backup Power Status   Normal
    Backup Power Type   Batteries
    Cache Enabled Status   Normal
    Cache Ratio   100% Read / 0% Write
    Cache Size   512MB
    Backup Power Voltage   Info not available for this hardware platform

As you can see it doesn't give a charge % so I'm assuming (hate to do that but with the info I have what else can I do) that 'Normal' means it's charged.

We replaced the BBU modules about a week ago, they went from charging to 'normal' within hours, and have been this way since so I don't think it's going to 'automagically' change itself to the 50 / 50 ratio it was prior to the BBU replacement.

As an aside we bounced one of the nodes for an unrelated maintenance event and it now shows properly 50 / 50 on the cache, obviously I can bounce all of our nodes individually and hope the others repeat the change in cache status; I was hoping however there was a way to change it from the CMC or CLI without the need for a reboot.

Thanks!

Re: P4500G2 cache 100% Read / 0% write

derlendson — Wed, 02 Sep 2015 16:58:47 GMT

Updating to Solved for any interrested.

The fix does require either:

A) system reboot

B) HP to remote in to the back end and change the cache settings.