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June 02, 2008


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Dave M

Great post Steve - very informative!

One sentence out of this article raises a question my teammates and I have been debating for some time...

"The cache would periodically be disabled and the BBU instructed to test itself."

So, on a CX3 series array, does write cache actually get disabled if/when a single SPS fails?


Steve Todd


Great question, you correctly point out that my historical blogging goes back to the days of only one BBU, where today's product uses 2 SPS (standby power supplies).

FLARE's behavior in today's systems is to keep the cache enabled when one of the SPS faults or tests itself.


Hi Steve,

I don't know much about Clariion so this might be a silly question. The Clariion write cache is actually a different hardware cache or it is a part of Main Memory of the storage processors?
And when there is a power failure, the BBU shuts down everything else but the SPs and the first 5 disks, is that so?

Steve Todd


The CLARiiON write cache is part of the main memory of the storage processors. So FLARE has to manage carving the memory between caching usage and FLARE's operational usage.

Regarding the BBU, as designed it needs to keep up the storage processors and 5 disks only. Keep in mind that today's CLARiiON use two SPS devices (standby power supplies) that operate in a similar fashion.


Andrés Suárez González

I suppose the 2 GB "module" for the CLARiiON dual storage processor is in more modern days than 1994, isn't it? Just curiosity for the real number...

Steve Todd

Hi Andres,
Yes you are correct, the latest CLARiiON to ship in August of 2008 has a maximum of 32GB of cache.

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