That's what I am thinking. Actually I haven't had any experience yet with AX, but with Clariion this sure was the case (maybe it even still is - I haven't been working with Clariion in more than 2 years).

I think a 2nd SPS will do the trick indeed, but just wait for a 2nd opinion to be sure.

Hello,

Only one SPS is required for write cache to be enabled on the AX4. Write cache requires two storage processors with no faults, no faults on the first 4 drives in the DPE, and a fully charged SPS connected to one of Storage Processors. If this is the first time you have powered on your system, write cache will be disabled because the SPS is still charging. You can check for this situation by logging in to Navi Express and expanding the DPE to look at the components. The SPS will show as Transitioning (Charging) for about 5-10 minutes, at which point write cache will be enabled automatically. This will be the case every time the System is powered on or rebooted.

Again, only one SPS is required for write cache on the AX4 (check that the SPS is connected to the system properly by verifying with the cabling diagram) but two are supported. If you ordered two SPSs and only received one, you should place a service call to check on the status. The Storage Processor that is not connected to the SPS should be powered from a different source. Only one SP power supply should be plugged into the SPS (the other outlet should be unused.)

To Further clarify my answer, Storage Processor A should have the SPS sense cable connected to it (mini serial cable that came with the SPS), and Power Supply A should be connected to the SPS. The Power Supply for SPB should be connected to a different power source than the SPS for high availability.

Just to verify (for my own knowledge):
is the 2nd SPS needed on the CX or CX3 series then for write caching to be enabled ? If not anymore at the moment, was this the case a few years ago ?

I think I've seen a "Clariion builder" which "said / mentioned" that the 2nd SPS was needed for the write cache to be enabled. It had something to do with safetely in case of power failure and that the cached writes had to be destaged to the vault. Only 1 SPS was considered not to be HA, so IMHO therefore write cache was not an option with 1 SPS.

Correct me if I'm wrong pls.

With regards to power, in order for Write Cache to enable, the base enclosure needs to be receiving AC power at both power supplies (for redundancy), and there needs to be at least one fully charge SPS unit detected (for vaulting the contents of Write Cache to disk in the event of an AC outage). There are platforms that are always configured with dual SPS units (e.g. CX700, CX3-80); and there are other platforms that are by default configured with a single SPS unit (e.g. AX-series, CX3-10) usually with a second SPS unit available as an option.

Regards,
DGM

ok sorry it took me so long to post a response. after trying multiple times to get the write caching to work with only one battery in an SPS i was unsuccessful. only after adding a second battery and connecting it to SPB was i able to get write caching to work. i have kicked this up the chain at EMC and should have an official answer in the near future. i will post the answer when i get it (please don't hold your breath).

It seems I was right