5 Replies Latest reply: Dec 26, 2012 11:58 PM by jianxunc RSS

Boost Your Storage IQ with Intelligent Caching

woods NetApp Employee Sprinter
Currently Being Moderated

This week I spoke with an IT director who bumped up the performance in his SAP application by fronting an HDS disk array with NetApp  V-Series and Flash Cache (PAM II) cards. The disk array had been a performance bottleneck for this transactional workload but he couldn't add any more spindles to increase the IOPS.  Flash Cache was like an extra strength aspirin tablet that ended a big headache for him.

 

Intelligent caching with Flash Cache gives you a way to decouple storage performance from the number of spindles in the underlying disk array to substantially improve cost, and reduce power, cooling and space requirements.  In a recent Tech OnTap article, we described the technology behind NetApp Flash Cache (PAM II) and demonstrated how using Flash Cache can cut costs by 50% or more while improving performance.  Our article also identifies the applications and environments where Flash Cache makes a strong contribution. You can check out this article at http://communities.netapp.com/docs/DOC-6508?REF_SOURCE=tot-1008

 

Also, please let the Community know if you are using Flash Cache or PAM caching modules.  We'd like to hear about your experience!

 

- Mark Woods

  • Re: Boost Your Storage IQ with Intelligent Caching
    hdiseguros Novice
    Currently Being Moderated

    Hi Mark.

     

    Our company is "budgeting" , planning to buy next year PAM II, today we use PAM I 16GB and almost nothing is cached, using metadata mode only.

     

    One article we are discussing internally is the WP-7082-0809 by Stephen Daniel and  Saad Jafri, August 2009. Our system is the same system used in test setup, FAS3160 and the same amount of disks (84) - 6 shelves.

    What I didnt understand in this paper is how they calculated the 31,500 IOPS, they say here 15K rpm 300GB highperformance disks. Are these disks different from 450GB 10KFC disks ?

     

    My system tops at 10K IOPs and we suffer from OLTP latency as well.

    • Re: Boost Your Storage IQ with Intelligent Caching
      woods NetApp Employee Sprinter
      Currently Being Moderated

      Let me start with a correction to the Tech OnTap article.  It mentioned a forthcoming technical report called “Using Flash Cache with Exchange 2010”.  The wrong report number was provided. It should have been TR-3867.  Here is the URL: http://media.netapp.com/documents/tr-3867.pdf

       

      Regarding your experience with PAM I … I recommend that you return to the default (“Normal”) mode of operation in which both metadata and user data are cached.  This the appropriate mode for OLTP.  The metadata mode is meant for situations where you have large numbers of objects with lots of associated WAFL metadata, such as an image repository.

       

      Check out TR-3832 “Flash Cache and PAM Best Practices Guide” for information about the modes of operation and the commands to use when changing modes.  http://media.netapp.com/documents/tr-3832.pdf

       

      About the OLTP white paper … The 31,504 IOPS reported in the white paper was not calculated. This is a measured result, as are the others.

       

      The difference between a 10k RPM and 15k RPM disk drive is significant under an OLTP workload. Data will be located and read more quickly on the faster spinning disk drive.  15k RPM drives typically yield 25% higher IOPS than 10k RPM drives.  (Your mileage may vary).

       

      Another tool we provide can help you figure out whether your storage system will perform better with more cache is a feature built into Data ONTAP. It’s called Predictive Cache Statistics (PCS).  The version in 7.3.3 is much improved from a usability standpoint compared to the original version.  This tool can help you to determine whether you will benefit from adding cache and how much to add.  Check out  TR-3801 “Introduction to Predictive Cache Statistics”.  http://media.netapp.com/documents/tr-3801.pdf

       

      Hope this info helps!

       

      - Mark

      • Re: Boost Your Storage IQ with Intelligent Caching
        hdiseguros Novice
        Currently Being Moderated

        Thankyou Mark

         

        I was finding very difficult to choose beetween metadata mode or normal mode, since my 16GB of cache dosent cache a lot. With metadata mode we have more hit %, about 20-30, with normalmode the hit % dosent go above 5%, but the number of blocks hit is about the same, like 1% of normalmode = 5 % metadatadamode, but I dont know which one is beneficing more the system.

         

        Reading this WP I was curious to know if thie 15K 300GB is faster than mine 15K 450GB disks, since I cant reach this 31.500 IOPS here.

        The guideline I found was that 250-300 IOPs per disk.

        • Re: Boost Your Storage IQ with Intelligent Caching
          woods NetApp Employee Sprinter
          Currently Being Moderated

          Sorry for the delayed reply. I wanted to consult with one of our engineers about your situation.

           

          There might be a small performance difference between a 300GB and 450GB  sizes of 15k RPM drives. However, it would be too small to justify  changing drive sizes.

           

          The data you have collected shows that metadata mode is clearly working better than "normal" mode. Stick with that for now. If you buy a larger caching module, or add more PAM cards, then I would try normal mode again.

           

          A larger cache (e.g. PAM II / Flash Cache) could help. You can check this before buying by running the Predictive Cache Statistics (PCS) feature under the actual workload.  You will need to turn off the PAM card to get valid results with PCS..

           

          I also recommend that you contact the technical person on your NetApp sales team to get his or her opinion.

           

          Best regards,

           

          Mark

  • Re: Boost Your Storage IQ with Intelligent Caching
    jianxunc NetApp Employee Novice
    Currently Being Moderated

    Hi One of our customer ask me, which GUI Tool can monitor FlashCache to collect Performance Data, and how can I do, if I want to know "How many IOPS is owned by FlashCache", in another word, how many Read OPS read data from FlashCache? Thank you very much.

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