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Removing disk units from configuration using SST

  • 1.  Removing disk units from configuration using SST

    Posted Wed October 02, 2024 12:22 PM

    Hello. Has anyone every used the SST option "Work with removing units from configuration" to remove disks that are in a RAID5 parity set?  

    We are hoping to make several drives non-configured in order to use them for an IASP. (We are planning to employ PowerHA eventually.)

    I'm just wondering whether or not it will work OK and wondering what I can expect. 

    We are on a Power9 41G at V7R4. We have 17 spinning drives in one RAID set with a hot spare. So the system unit is at capacity as far as disk, and we do not have an additional disk enclosure. We are only running at 41% usage on the system ASP so there is plenty of room to take some drives for the IASP.

    Incidentally, I did ask IBM hardware support about this but I am interested to hear of real-world occurrences.

    Thanks,

    John



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    John Paisley
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  • 2.  RE: Removing disk units from configuration using SST

    Posted Wed October 02, 2024 05:08 PM

    Dear John,

    It is quite a while since i have used internal disks for IBM i. We are using external storage connected to IBM i so we are just removing and added disks whenever needed. Please refer to the link below which might be helpful in your case.

    Removing disk units that have device parity protection from a disk pool with mirrored protection - IBM Documentation

    Once the disks are removed these will be available as non-configured disks and visible for the addition to IASP.  You also need to think if you will add these disks to IASP without protection or with protection as it will be another storage pool on your system. 



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    Rohit Chauhan
    Senior Technical Specialist
    Norway
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  • 3.  RE: Removing disk units from configuration using SST

    Posted Wed October 02, 2024 10:05 PM
    Edited by Satid S Wed October 02, 2024 10:14 PM

    Dear John

    >>>> We are hoping to make several drives non-configured in order to use them for an IASP. (We are planning to employ PowerHA eventually.) <<<<

    Do you want to create a new RAID-5 set for the new IASP  out of these removed disk units?  IIRC, removing disk unit from an existing RAID-5 set may need to be done in restricted state which means a disruptive action. (If it can be done on-line, your disk response time during the removal can be dismal to the point of not being able to run your workload and the more units you remove from the RAID-5 set, the longer this situation lasts.)   I hope you are ware what you asked about is NOT mandatory. 

    You can just remove some disk units out of your existing system ASP without removing them from the underlying RAID-5 HW and then create the new IASP out of these removed units.  This is convenient as, since IBM i 7.1, disk unit removal from an ASP can be done on-line without a need for an IPL as the last step.  You will not be able to remove as many units for now for the new IASP but, once you migrate all core app data out of System ASP, you will be able to remove more units out of System ASP and add them to IASP later (be sure to run STRASPBAL  *CAPACITY for the IASP after disk unit addition).

    Having a separate RAID-5 set dedicated for the new IASP may appear a better approach but I doubt if it is actually sufficiently beneficial since you already have a hot spare for your current RAID-5 set.   You are likely not able to afford any hot spare disk with 2 RAID-5 sets and this may reduce the practical benefit of having 2 RAID-5 sets.  

    Hope this supplies you with relevant information for your case.



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    Satid S
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  • 4.  RE: Removing disk units from configuration using SST

    Posted Fri October 04, 2024 06:42 AM

    Thank you both for your replies! It is much appreciated.

    I am not so much concerned about creating an additional RAID-5 set for the IASP drives. As long as I know that it will work OK with both the SYSBAS ASP and the IASP in the same existing RAID-5 set, I am satisfied with that.  All of the disks will be protected by RAID-5 with hot spare. 

    I think you have answered my question, Satid, as to what I can expect from the remove procedure in SST:

    The disks will show up as non-configured but the RAID set will be preserved as it was.   Please correct me if I'm wrong.

    This would be a convenient method, as you said.

    Thanks again!

    John



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    John Paisley
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  • 5.  RE: Removing disk units from configuration using SST

    Posted Fri October 04, 2024 07:24 AM

    I think you must assure that the load disk is not removed from the original ASP.

     

    Best Regards

      

    -------------------------

    Andreu Rul

    CTO

    Telf: +34 663 817 144

     

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  • 6.  RE: Removing disk units from configuration using SST

    Posted Fri October 04, 2024 07:32 AM

    Thanks for that tip, Andreu! I will make absolutely sure that I know which disk is the load source.

    John



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    John Paisley
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  • 7.  RE: Removing disk units from configuration using SST

    Posted Fri October 04, 2024 08:34 PM

    Dear Andreu and John

    >>>> I think you must assure that the load disk is not removed from the original ASP. <<<<

    This is not to worry about at all because the SST tool DOES NOT show the load source disk (disk unit number 1) in the screen for disk removal from ASP as shown below: 



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    Satid S
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  • 8.  RE: Removing disk units from configuration using SST

    Posted Mon October 07, 2024 02:58 AM

    Hi all,

    If you want to move Load Disc, you have to stop the system, perform a manual IPL and then in DST copy Load disc. 

    So, it's not possible to "remove form configuration" in SST in running state. The only action you can do if you want to move user data from load disc to other discs in the *SYVAL ASP is  STRASPBAL TYPE(*ENDALC) UNIT(1) and then STRASPBAL TYPE(*MOVDTA) TIMLMT(minutes you want)

    Regards,



    ------------------------------
    Eduard Marco Galindo
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  • 9.  RE: Removing disk units from configuration using SST

    Posted Mon October 07, 2024 02:50 AM

    Hi John,

    Correct, you don't lost RAID protection if you use this option (removing units from configuration). This option only removes discs from ASP where they are located.



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    Eduard Marco Galindo
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  • 10.  RE: Removing disk units from configuration using SST

    Posted Mon October 07, 2024 10:18 AM

    Thank you, Eduard, for confirming this.

    John



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    John Paisley
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  • 11.  RE: Removing disk units from configuration using SST

    Posted Fri October 04, 2024 11:25 AM

    Hi John, 

    For precaution, don't forget to back up your system before removing disk. 

    I'm not familiar with your production and don't know why 17 disks were needed on the system at startup, but from what I always hear from IBM and for the IBM i in particular the more arms (disks) the better for performance (i/o). So by removing disks from the cluster, you may be increasing processing times. You might want to run a performance analysis before doing so, to confirm that removing disks will not impact your production.

    Regards



    ------------------------------
    Virgile VATIN
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  • 12.  RE: Removing disk units from configuration using SST

    Posted Fri October 04, 2024 09:06 PM

    Dear John

    >>>>  You might want to run a performance analysis before doing so, to confirm that removing disks will not impact your production. <<<<

    For this purpose, you can use the tool IBM i Performance Data Investigator (PDI) from Navigator for i GUI.  Use the performance chart named Disk Throughput Overview for Disk Pools and Physical Disk IO Overview - Basic that look like these:

    The point is to take note of disk response time at peak MB/sec. and peak Disk IOPS period(s). If response time does not degrade too much higher than 5 millisec. (I assume HDD rather than SSD here) and/or is not so for a long period of time (say, less than 15 minutes), you are still in good shape.   You should look at these charts at peak workload day(s) and you should look at them BEFORE and AFTER you implement PowerHA for i for comparison. 



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    Satid S
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  • 13.  RE: Removing disk units from configuration using SST

    Posted Mon October 07, 2024 12:52 PM

    Thanks again Satid. Based on the chart below, which was taken on a typical busy day, Wed, Oct 2nd, it looks like we are in pretty good shape for the time being - pre-PowerHA.  Although, I am not sure what equates to "response time". Is it "Average Service Time" or "Average Wait Time" or a combination of the two?

    Thanks,

    John



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    John Paisley
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  • 14.  RE: Removing disk units from configuration using SST

    Posted Mon October 07, 2024 08:29 PM
    Edited by Satid S Mon October 07, 2024 08:37 PM

    Dear John

    >>>>  I am not sure what equates to "response time". Is it "Average Service Time" or "Average Wait Time" or a combination of the two? <<<<

    You have a good question.  Disk response time normally means service time + wait time. If you see a lot of wait time in both msec. and frequency of its occurrence that also correspond to occurrence of high disk IOPS, you need more disk units.  Your case above is not bad yet because the chart indicates that your disk IO workload of MB/sec. is generally very low.  If disk IO workload increases in the future, and you see more wait time in conjunction with high IOPS, it's time to either add more disk units or if you have a lot of SQL/Query workload, to look at index advisor of large physical files and create useful indexes which will help reduce total disk IO workload and therefore disk response time.

    That bad response time of about 9 msec. at 10:30 AM should not be a big concern as it lasted 15 minutes or less and I suspect it may happen due to a burst of high disk IOPS.  You should produce the Physical Disk IO Overview - Basic chart as well to see disk IOPS profile and use it in association with Disk Throughput Overview for Disk Pools chart.  Then look at them again after PowerHA is in operation or when users complain of slow workload performance.



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    Satid S
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