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I brought a HP Smart Array P410 controller and it is installed and working fine in a HP Prolient Microserver with 4 drives in two RAID 1 arrays.

I didn’t realise however that it came without any cache so would only work by directly writing straight to the disk, and the performance was horrible.

So I then brought the 512MB Flash Backed Write Cache (FBWC) memory module as I was under the impression that with FBWC I would not need a battery. I got this idea from a forum post.

"What do you guys think of the choice between 'BBWC' (battery backed write cache) and 'FBWC' (flash backed write cache)? The flashed based ones use non-volitile memory so need no battery."

After installing the cache module however the server pretty much won’t boot. The P410 has a flashing amber light on it, and from the manual that doesn’t sound good. I’ve managed to get to the on board BIOS once and even managed to get to boot to the HP Array Configuration Utility (ACU) CD once, but every other time the Server continuingly reboots once it get to the POST screen and reads ARRAY INITILIZING %%%.

The one time I reached the ACU, it reported a problem with the Cache Module.

To me, it seems like the cache module is faulty, however the supplier tells me

“Do you have an FBWC battery pack, p/n 587324-001, because that is required for the cache to work. If you have it, please complete an RMA form and we'll send a replacement / credit.”

Does this sound right to you? I’ve been ordering the parts from the US and I don’t want to spend $77 + $40 p&p on a battery, wait a week for the shipping to find the card is faulty, and I don’t want to send back a working card?

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The FBWC requires a power source to allow it to write the cache to flash in the event that the power fails. Typically, a large capacitor is used for this purpose. –  David Schwartz Oct 4 '12 at 5:18
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1 Answer

up vote 4 down vote accepted

You were correct in understanding that the write cache solution would help performance. However, you just didn't order the right parts. What you ordered was a 512MB chip. The reason the flash capacitor is external to the memory module/RAID controller is to preserve the old form-factor of the older battery-backed module (forward-compatible). The part number should have been #534916-B21 and should have included everything listed below:

If you don't have both parts pictured here, your solution won't work.

Left: RAM module. Right: External flash capacitor. enter image description here

The capacitor unit is pretty key to the operation. Where did you buy this from? Nobody sells the memory module alone unless it's ordered as a spare or repair part.

In general, when ordering HP, look at the quickspecs for the product you wish to buy. In this case, the Smart Array P410 quickspecs would have given you specific part numbers (and compatibility notes) to make your solution whole.

Non-volatile cache RAID controllers: what kind of protection is there against NVCACHE failure?

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Many Thanks. I was buying the parts refurbished from ebay in order to keep costs down, but slightly false economy when you consider the $100+ in P&P over the 3 orders. What I was missing was somewhere on the web was a simple buying guide. So note to anyone else, if you buy a 512MB Flash Backed Write Cache (FBWC) memory module, you need to buy the capacitor as well. –  Martyn Oct 4 '12 at 21:51
    
@Martyn Actually, they just need to buy part #534916-B21, and they should be fine. –  ewwhite Oct 4 '12 at 22:05
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