Yes it is 100TB for a single LPAR of IBM i. If using internal disks which is not achievable for this kind of size. The only option is to use external storage.
I did a run test on different total of LUNs, the more LUNs the better performance on bandwidths and IOPs.
Original Message:
Sent: Wed January 24, 2024 08:08 AM
From: Robert Berendt
Subject: How much LUN is required for an IBMi partition?
I'm a little confused by "Does the rule of thumb still the same if the IBMi machine running multiple LPARs?"
I'm not being petty on semantics but there is no such thing as an "IBM i machine". It would be a Power system running multiple LPARs of IBM i. The reason I'm saying that this is not just semantics is that I want to be sure that you are not planning on having all these luns go to one lpar of IBM i and then hosting the other partitions of IBM i off of that lpar.
For internal disk we did host all the drives from one lpar of IBM i to the other lpars of IBM i (and AIX). When we went to SAN we eliminated that hosting partition of IBM i.
Now each lpar of IBM i has their own luns (hosted through vios) from the SAN.
I did pull down that redbook. I found the section you mentioned. I think you have a rather unique scenario and I wonder what the authors would do if it was presented. 100TB is quite large. The redbook mentions "...and up to a few hundreds for large partitions." If you take 150GB luns, which only appear as 143GB drives on the lpar of IBM i, and divide 100TB by 143GB you get 699 luns. Let's just say 700. I think that qualifies as more than "a few hundreds".
That 100TB, was that just for one lpar of IBM i, or was it for all lpars of IBM i? Big difference.
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Robert Berendt IBMChampion
Original Message:
Sent: Mon January 22, 2024 05:40 AM
From: wong ck
Subject: How much LUN is required for an IBMi partition?
Dear Satid and Martin,
Very grateful on the valuable feedbacks.
Are my assumptions correct if an IBMi lpar running on an external storage with full of NVMe disks.
1. We should care total of LUNs to create instead the size of the LUN.
2. IOPs is leverages on the storage instead of server. Server mainly control the bandwidth of FC cards.
Does the rule of thumb still the same if the IBMi machine running multiple LPARs?
I was reading below Redbooks.
Performance and Best Practices Guide for IBM Storage FlashSystem and IBM SAN Volume Controller
Updated for IBM Storage Virtualize Version 8.6 - 2023
Defining LUNs for IBM i
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wong ck
Original Message:
Sent: Mon January 22, 2024 01:19 AM
From: Satid Singkorapoom
Subject: How much LUN is required for an IBMi partition?
Dear Wong
In my long experience with IBM i disk performance, there is no hard and fast rule for an answer but the general principle is that IBM i likes many disk units/LUNs. More units are needed for spinning disk case than SSD case. LUN size does not matter much for IBM i.
I agree that 500 LUNs can be overkill but if this can be done without much hassle on the part of whoever will do the set up of all the config involved, it can be fine. Otherwise, you can reduce down to around 100 LUNS or so.
How many CPU cores are allocated to IBM i LPAR? I would suggest some 15 disk units/LUNs per Power10 core for SSD case for a case of heavy workload and your case may exceed this by a lot already.
By the way, which IBM redbook did you refer to? I guess its quite an old one because IBM i also has spinning disk units larger than 200GB (even TB-size one) for many years already before the arrival of SSD.
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Chance favors only the prepared mind.
-- Louis Pasteur
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Satid S.
Original Message:
Sent: Thu January 18, 2024 10:37 PM
From: wong ck
Subject: How much LUN is required for an IBMi partition?
I have a FS7300 attaching to an IBMi lpar. A total of 100TB will be assigned to that LPAR. How much LUN should I create?
From redbooks, it mentioned "You should not define LUNs larger than about 200 GB" for IBMi.
A rough calculation, a total of 500 LUNs will be present at IBMi lpar. This 500 figures seems alot, is this calculation is correct? Is there any guideline?
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wong ck
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