VM 123 qmp command ‘block_resize’ failed – iSCSI: failed to send readcapacity10/16 command (500)

Whilst trying to enlarge a Proxmox VE iSCSI TrueNAS attached disk to a PBS server, you might encounter the following problem:

VM 123 qmp command 'block_resize' failed - iSCSI: failed to send readcapacity10/16 command (500)

Check the console, you might be having disk issues:

[42038.811934] 1/0 error,dev sca, sector 34544392 op OxO: (READ) flags 0x0 phys_seg 1 prio class 2
[42698.916526] I/D error dev sca, sector 34544392 op OxO: (READ) flags 0x0 phys_seg 1 prio class 2 dev sda, sector 34544392 op OxO: (READ) flags 0x8 phys_seg 1 prio class 2
[42098.996477) I/O error, dev sda, sector 34544392 op 0X0: (READ) flags 0x8 phys_seg 1 prio class
[42159.085032) I/D error, dev sda, sector 34544392 op Ox@: (READ) fLags 0x8 phys_seg
(42159.165077) I/D error,1 prio class
(42169.501148]dev sda, sector 34544392 op OxO: (READ) flags 0x0 phys_seg 1 prio class 2 I/0 error , sector 80419576 op OXO: (READ) flags 0x9000 phys_seg 1 prio class 2
[42219.395619) I/D error, Dey sea , sector 34544392 op exo: (READ) fLags axe phys_seg "OO ClaSS
[42219.3855721 I/D error dev sda, sector 34544392 op

Try to gracefully shut down the machine, and then try again.