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SVC 7.3 Cache Questions

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Question by T_IBM2002  (5) | Aug 17, 2016 at 02:50 PM svcsan_volume_controllerv7000spectrum_virtualizespectrum control

Hello, I have a few questions concerning the SVC 7.3.x cache architecture. I'm trying to utilize TPC (Spectrum Control) to get idea if there are any cache constraints in my environment.

Client Setup: 8 CG8 nodes with dual FC cards, cluster running 7.4.x. , global mirror, no RTC, 20 Storage Pools. Behind this cluster are six v7000's GEN1 with 20+ storage pools each hosting 1 volume. No performance complaints.

  1. TPC reports cache statistics for Volume Cache (VC) and Volume Copy Cache (VCC). Please confirm which cache is the upper / lower.

  2. I understand SVC 7.3 has split the cache between upper (front-end) and lower. Is it true that lower cache only exists / is utilized if a vdisk is being mirrored?

  3. There is a third party reporting tool that claims to show "Cache Fullness". for SVC/V7000, Is there an equivalent metric to look at in TPC/Spectrum control.

  4. Which TPC metric is most useful in revealing cache constraints.

Thank You.

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Answer by IanBoden (126) | Aug 18, 2016 at 04:55 AM

  1. Volume Cache is the upper cache, Volume Copy Cache is the lower

  2. The lower cache is utilized for all cache enabled volumes regardless of how many copies they have

  3. As far as I know the latest version of Spectrum Control still does not show the fullness, if you can't find an RFE to add this statistic to add a vote to, then please open one.

  4. This is a bit hard to answer, as it will depend on what you are trying to achieve. For some the read hit percentage is the most important, for others they are more concerned about write bandwidth or write latency. Personally I like monitoring the fullness but as you have discovered that isn't currently possible though Spectrum Control, that gives an indication of what kind of burst of writes the system is capable of absorbing.

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