weird behaviour with passtrough disk after removal

RolandK

Renowned Member
Mar 5, 2019
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hello,

i have made some weird observation with passtrough disk in proxmox (scsi12)

i'm using these for a long time in different scenarios and there were no problems so far.

today, i wanted to replace a faulty disk, because the existing one had read-errors.

i know that it's not meant to pull a disk from the system when it's in used by a VM via such direct mapping (normally i do a VM shutdown) , but i wonder why i had this result.

after setting the device offline inside the VM (zfs), i started read with dd inside the VM to identify which phyiscal disk needs to be pulled (by constant flashing led). then i pulled that disk

for my curiosity, i could still successfully read at a rate >200MB/s from that disk, and it seemed to be the data was all zeroes. i could even restart the dd and it did read further...

when trying to write a single byte to the disk inside the VM, the VM crashed and was marked yellow with "IO error" in proxmox

why does block level failure with passtrough disks work without a problem (i.e. read/write errors being passed to the guest and no io-error at proxmox gui) and why does device level removal behave so different ( zero reads , io-error in proxmox on first write) ?

regards

this is my configuration for the disks
```
scsi0: vms-files:100/vm-100-disk-0.qcow2,aio=threads,discard=on,iothread=1,size=20G
scsi10: /dev/disk/by-id/ata-ST12000VN0007-2GS116_ZCH0BJZJ,aio=threads,backup=0,detect_zeroes=0,iothread=1,size=11176G
scsi11: /dev/disk/by-id/ata-ST12000VN0007-2GS116_ZCH0BLQE,aio=threads,backup=0,iothread=1,detect_zeroes=0,size=11176G
scsi12: /dev/disk/by-id/ata-ST12000VN0007-2GS116_ZCH08ZZG,aio=threads,backup=0,iothread=1,detect_zeroes=0,size=11176G
scsi13: /dev/disk/by-id/ata-ST12000VN0007-2GS116_ZCH06MCP,aio=threads,backup=0,iothread=1,detect_zeroes=0,size=11176G
scsi14: /dev/disk/by-id/ata-ST12000VN0007-2GS116_ZCH06YW5,aio=threads,backup=0,iothread=1,detect_zeroes=0,size=11176G
scsi15: /dev/disk/by-id/ata-ST12000VN0007-2GS116_ZCH0BJPE,aio=threads,backup=0,iothread=1,detect_zeroes=0,size=11176G
scsihw: virtio-scsi-single
 

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