Adaptive Flash Cache on 3Par 7200

[letisistemas]

Hello

We have just installed a brand new 7200c 3Par (storeserv :P ), with 4 cages, one of them for NL disks.  On the other 3 there are 36 600GB 15k FC disks and 12 480GB SSD

Initially, our idea was to use 8 of the SSD disks for tiering with the dynamic optimization, and use the other 4 SSDs to built a flash cache extension with the adaptive flash cache feature.

The "problem" (is not critical, but I would like to know if it has a solution), is that we don't know how to dedicate these four disks to cache. When enabling flash cache system spreads the amount asigned on all 12 SSDs, althoug we created a CPG with 8 disks and left 4 "free"

After that , we decided to add all disks to CPG and use them at same time for tiering and flash but I think is not optimal to maximize performance, and I would like to separate 8 disks for tiering and 4 disks for caching.

Is this possible????

Thanks.

Dave.

[Cali]

There is no way to create flash cache (createflashcache) and specify a particular set of SSDs.

But flash cache and CPG can coexist.

Note:

480GB cMLC are not supportet for flash cache.

[letisistemas]

My disks are MLC, not cMLC, they are supported and, in fact, we have activated the flash caché succesfully on them, but I thought it was possible to dedicate disks to this feature :(

And so, at this point....  which size is recommended or reasonable to use??  Is a 1,5TB (768GB per controller) overkill or it would be usable??? I say 1,5TB because is more or less the size planned before deployment when we bought (because our retailer recommended), 4 more disks for caching.

Regards.

Dave.

[Cali]

You can use

createflashcache –sim xxxG

and then look with statcache and srstatcache for the FMP Values.

So you can test it with different Sizes and find the best for you.

But consider that the Cache may need a long Warmup time.

I prefer to use Tiering only, with Tiering everthng that is hot is on SSD and can do wite on SSD too.

If have greatest Performance on my Customers with only SSD Tiering.

[Sheldon Smith]

Since you have the SSD, activate the flashcache with the initial planned size. After you have all of your planned production load moved to the system, allow some time for the cache to "warm up".
I'd suggest that if after a week of full production, you are getting good hit rates but the flashcache is not full, re-create it smaller.