[pve-devel] scsi-hd vs scsi-generic with iSCSI

[Dmitry Petuhov]

Hello

09.10.2019 18:39, Thomas Lamprecht wrote:
> I would actually really like to change this to scsi-hd, but we need to 
> be sure
> it's OK for all possible supported setups..
>
> So I tried to investigate a bit how it came to the use of scsi-generic, I came
> to a commit[0] from Alexandre (CCd) which adds support for access with libiscsi.
>
> Maybe he knows why the -generic was used and not the -hd one?
Maybe it was slightly faster. With scsi-hd, qemu fully emulates hard 
disk, including all capabilities and with scsi-generic/scsi-block it 
just pases all scsi commands from guest to iscsi layer without translation.

So there may be issues on migration if backing storage is, say, 4k 
block. In this case with scsi-generic it appears in guest 4k, but 
scsi-hd will emulate legacy 512-byte block sizes, making filesystem 
inaccessible.


> [0]:https://git.proxmox.com/?p=qemu-server.git;a=commitdiff;h=d454d040338a6216c8d3e5cc9623d6223476cb5a
>
> cheers,
> Thomas
>
>
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