3PAR: configure AFC with SSDs only for AFC

When initialize a new 3PAR, depending on your protection level, at least the size of one disk per disk-type will be reserved as spare. Also when you add disks to a running system, spare-chunklets are created. This is done by admithw. For example when you initialize a system containing 2 SSDs for adaptive flash cache (AFC) the size of one SSD is reserved for spare. So without writing any byte to SSDs, 50% is already used! So how to be able to get the most space for AFC? This post is about how to configure 3PAR adaptive flash cache when SSDs are used for AFC only.

  1. Check the capacity of you physical disks (PDs) by running showpd -c. You see free and used chunklet-counts. Also spare-chunklet are listed.
  2. Remove spare-chunklets from disk by running: removespare n:a. n stands for PD-ID of your SSD.
  3. Check again capacity by running showpd -c. You can see, free is the same as before, but uninit is the size of previous spares.
  4. Wait a few minutes and you can see, uninit decreases and free increases. Chunklets get initialized automatically.
  5. When all chunklets are initialized and therefore free, go ahead and create cache for AFC in GUI or CLI (createflashcache). SSMC needs a few minutes to see new free space on PDs.

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