Dear Adrian
If the new Power10 uses SSD from (presumably another new) SAN, it can be a performance improvement over the old disk HW. One thing on the SAN is NOT to use Data Reduction Pool feature for production workload as DRP imposes performance overhead to disk response time as I discussed in my article that you can read here: Guru: IBM i Experience Sharing, Case 3 – When Performance Issues Come From Without at https://www.itjungle.com/author/satid-singkorapoom/
>>>> This is one of my concerns since some LPARs are small like 2,000 CPW or less which is less than 0.1 of a Power 10 core. I'm afraid allocating 0.0x cores and get poor performance. <<<<
As for your concern on Power10 CPU allocation. keep in mind that with automatic CPU GHz adjustment according to incoming workload since Power8 time, actual CPW per core is not fixed and I assume the published figures from IBM are always at the highest GHz only. And if you ever watch WRKSYSACT screen in any small workload LPAR since Power8 time, you may notice that "Average CPU Rate" can show a value less than 100% most of the time which means CPW per core you use from published figures can be too high for your sizing. For Power10, I personally use only 20,000 CPW per core for sizing purpose. In such as case, you allocate 0.13 CPU for 2,600 CPW that you originally mentioned. And if there are more than 1 LPAR in the server, using Shared Processor Pool and Uncapped Partitioning can help with flexible CPU power usage. Does my description here make sense to you?
And when VIOS is used for NPIV (vFC) connection to SAN disk, be sure VIOS is allocated proper CPU power. I used to encounter IBM i LPAR seeing much degraded disk response time (0.5 degraded to 3 msec.) during its batch run period which was its daily peak workload. Since the disk is from SSD from FS5K SAN. such a response time degradation is considered bad and should be addressed. VIOS served 3 non-production IBM i LPARs (Development, Integration Test, and UAT) with many programmers and users accessing UAT mainly. It turned out VIOS got only 0.5 CPU allocation and its CPU is 100% busy during the batch run! Increasing VIOS CPU allocation to 1 made disk response time consistent throughout the entire day workload.
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Satid S
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Original Message:
Sent: Tue April 02, 2024 08:43 AM
From: Adrian Francis Puno
Subject: Sizing an LPAR
Hello Satid,
Origin LPAR could be from a spinning disk, and could be from SAN storage, but target would be on a Power 10 with SAN and VIOS.
I'm looking at Performance Navigator as suggested by Juan and it looks promising since it seems to work like the old sizing tool in GO PERFORM way way back in OS/400 Versions 4 and 5.
If you see that the existing 7.4 LPAR has no performance issue whatsoever, you just allocate similar CPW and memory to Power10 LPAR but you need to also make sure you configure equivalent or better HW config for disk resource.
This is one of my concerns since some LPARs are small like 2,000 CPW or less which is less than 0.1 of a Power 10 core. I'm afraid allocating 0.0x cores and get poor performance.
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Adrian Francis Puno
Original Message:
Sent: Mon April 01, 2024 09:04 PM
From: Satid S
Subject: Sizing an LPAR
Dear Adrian
Is the existing 7.4 LPAR running on VIOS? If so, what virtual resources the existing IBM i LPAR is using - vFC, vDisk, vLAN? Does the existing LPAR use internal disk/SSD or SAN disk?
Assuming no VIOS nor SAN disk is involved, you should check with the customer first whether or not the existing LPAR still performs satisfactorily for them at the peak workload periods. (Also look at some PDI charts on Wait Overview, Disk Response time and Memory Fault Rate to verify the customer's response.) If it is good, you next check whether or not the TR group PTF level is high enough for IBM i 7.4 to run in Power10 server and if not whether the customer allows you to apply any additional PTFs needed so that you can plan how to migrate the LPAR to Power10.
If the customer reports performance issue with the current LPAR, you need to review PDI charts to see where the performance cause is so you can see how you would adjust the HW resource on Power10 LPAR.
If you see that the existing 7.4 LPAR has no performance issue whatsoever, you just allocate similar CPW and memory to Power10 LPAR but you need to also make sure you configure equivalent or better HW config for disk resource.
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Satid S
Original Message:
Sent: Mon April 01, 2024 08:30 AM
From: Adrian Francis Puno
Subject: Sizing an LPAR
Hello,
Suppose I have a small V7R4 LPAR from a Power 8 with just 2,600 CPW and 16GB if memory. How would you bring it up to a Power 10?
Allocate 2,600 CPW and 16GB memory equivalent on Power 10 processor? Or do we have minimum sizing that I can follow?
Thanks
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Adrian Francis Puno
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