SG24-8062 (IBM PowerVM Best Practices) does mention using VSCSI to allow an IBM i to access 512-byte disks when you don't have 520-byte storage, but it's from 2012.
I can't find any reference if it maps a 512 520-byte sectors to 520 512-byte sectors (which would cause a large performance impact) or it strips/adds the 8 byte CRC to each sector doing 1:1 mapping (more likely).
Searches for "512 520 4096 disk block" seem to always land on the PLET/ALET...
Original Message:
Sent: Fri March 31, 2023 05:32 AM
From: Sylvain
Subject: Problem adding a new disk from IBM storage to a volumen group, mismatch disk block size
We use SAN LUN seen as PV on AIX.
Sometimes we also use LV as vscsi volume.
Both works well.
Original Message:
Sent: 3/31/2023 5:28:00 AM
From: José Pina Coelho
Subject: RE: Problem adding a new disk from IBM storage to a volumen group, mismatch disk block size
In that case, are you passing a PV, an LV, or an SSP volume as a VSCSI volume ? Note that the ability to use a 4096 volume with a 512 block size may go away anytime.
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José Pina Coelho
IT Specialist at Kyndryl
Original Message:
Sent: Fri March 31, 2023 05:20 AM
From: Sylvain
Subject: Problem adding a new disk from IBM storage to a volumen group, mismatch disk block size
Already tested several times.
It works perfectly.
Original Message:
Sent: 3/31/2023 5:09:00 AM
From: José Pina Coelho
Subject: RE: Problem adding a new disk from IBM storage to a volumen group, mismatch disk block size
alt_disk_copy will work (it doesn't use mirror&split, instead it uses mkvg/mklv/mkfs then copies the files to the new structure)
As to virtualizing through the VIOS, I don't know if it shadows the block size (it should), but even if it doesn't now, it will in the future.
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José Pina Coelho
IT Specialist at Kyndryl
Original Message:
Sent: Thu March 30, 2023 08:33 PM
From: Luis Alberto Rojas Kramer
Subject: Problem adding a new disk from IBM storage to a volumen group, mismatch disk block size
Hi Juan Jose
You cant add other new volumes to an Volume Group id the block size of the new one is not equal to existing disks.
That is a problem with new hard drives with 4KB block size when legacy and generally SAN disks use just 512B.
Unfortunatelly this is a fixed setting coming from the hardware and it is not possible to be changed.
I suggest you to do an mksysb and restore it on a new disk (LUN from SAN)
I don't know if alt_disk_copy could work for this, I understand the process is like to a mirrorvg and then a splitvg more than a backup/restore from a VG to another. So, it should need again add the new disk to VG first... (I don't pretty sure of this, you can try it)
It is possible to virtualize a file from VIOS to server to be seen as a new hdisk which broke with the fixed disk block size masking a new 512B device... but I do not recommend this because of performance and access redundancy.
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Luis Alberto Rojas Kramer
Original Message:
Sent: Thu March 30, 2023 12:07 PM
From: Juan Jose Morales Ortiz
Subject: Problem adding a new disk from IBM storage to a volumen group, mismatch disk block size
Hello everyone.
We want to mirror the rootvg on a SAN disk, but skip the next issue:
0516-1980 extendvg: Block size of all disks in the volume group must be the same. Cannot mix disks with different block sizes.
Is there any way to change the disk block zise on AIX disk (/dev/hdiskX) before to extend or add the new PV to the VG and get the mirror of the rootvg ?
Note: The disk where the OS resides is an internal NVMe disk.
Regards,
JJMO
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Juan Jose Morales Ortiz
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