IBM i

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  • 1.  External Storage with IBM i

    Posted Tue May 10, 2022 11:06 AM
    Hi,

    Question related to External Storage. I came to know FS9200/9500 comes with inbuilt hardware compression feature like 2:1. So if we need 50TB of external storage for our IBM i workload (OS+Date), with compression we need only 25TB of external storage usable capacity. Is this recommended ? Do we see some performance impact ? My understanding was that compression is used only for backup, not for production workload. Please share your thoughts.

    With Regards
    Angela B.

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    Angela B
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  • 2.  RE: External Storage with IBM i

    Posted Tue May 10, 2022 11:33 AM

    Hi

    Storage compression rate is related to the type of data stored onto the storage. E.g. If so just store plain text to tables you may even reach compression rates up to 80% if it's other data the compression rate will be less. 

    On the above mentioned storage you shouldn't see any performance impacts related to the compression as the HW is doing the compression. (Have a look at product guide https://www.redbooks.ibm.com/redpapers/pdfs/redp5586.pdf page 4)

    And yes HW compression on Flashs storage is something to enable for production. - At least that is the case with us.

    Markus



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    Markus Neuhold
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  • 3.  RE: External Storage with IBM i

    Posted Tue May 10, 2022 01:38 PM
    Hi Markus,

    Thanks for the insights. One question, as you know IBM i data will not be plain text, any idea how much compression rate I can expect. I have usable 50TB of external storage V7000 assigned to IBM i LPARs. Now we are planning for storage refresh with Flash System. I will go for 25TB of Flash System FS9200, considering 2:1 compression ratio. I hope my understanding is correct.

    With Regards
    Angela B.

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    Angela B
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  • 4.  RE: External Storage with IBM i

    Posted Tue May 10, 2022 10:24 PM
    Edited by Satid Singkorapoom Tue May 10, 2022 10:38 PM
    Dear Angela

    In my experience solving IBM i customers' performance problem of all kinds in the past 15 years or so, disk compression is more suitable for non-production workload or for production workload that you know for sure you have no high performance expectation for the critical part of the production workload.  Customers with disk compression who came to me for help were ones who had high expectation for the performance of critical part of their production workload, almost always batch process. 

    Disk space saving technology always reduce the peak disk IO throughput (IOPS and MB/sec) level which decent disk response time can be maintained while under these peak values. This peak disk IO throughput varies based on SAN HW config and compression features used. The best tool in IBM i to check if you have this problem or not is PDI charts of Disk category (please read my suggested article below if you are interested to learn more). 

    When you want to use any kind of disk space saving technology in a production environment with critical workload that you expect the best possible performance (especially batch process), you need to seek assurance from SAN vendor in the design of the disk HW for the best and consistent disk response time. It is best that you communicate with SAN vendor up front before you buy it if you have high expectation for consistent disk response time during your critical part of production workload.   For SSD/Flash disk system, you can use my personal rule of thumb for 2.5 msec (use 5 msec for HDD system) as the worst allowable disk response time you expect for your critical part of the workload and you use PDI chart to check on it once the system is in production.  For SAN HW design, the SAN vendor should need to know what your current peak disk IO workload is in terms of peak IOPS and MB/sec and you use PDI chart of your current peak workload day(s) to obtain this information. The design of the proposed SAN should be set to accommodate at least some 50% more of the current peak IOPS and MB/sec if you have no specific picture of your future workload growth..

    Please read this article of mine for a sample case of disk performance issue in IBM i using SAN with flash disk and disk space saving technology :  https://www.itjungle.com/author/satid-singkorapoom/   (look at case 3).

    Let me know if you have further questions.

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    Satid Singkorapoom
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