Re: [Xen-devel] Xen 4.3 development update CODE FREEZE HAS_BEGUN

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

On 18/04/13 21:58, Alex Bligh wrote:
> 
> 
> --On 18 April 2013 16:50:06 +0200 Roger Pau Monnà <roger.pau@xxxxxxxxxx> 
> wrote:
> 
>>  - The new iSCSI libxl/xl disk functionality could also be considered a
>> tech preview, again it's best to have it like that rather than not
>> having it at all, I've heard quite a lot of people asking about iSCSI
>> support in Xen.
> 
> I don't quite understand this point. We've been happily using iSCSI
> support (i.e. dom0 iSCSI block devices) with xen 4.2 for ages,
> using libxl. I am 99.9% sure we have this working with xl too for
> testing. Why does Xen even care whether /dev/sdc is a SATA disk or
> a SCSI disk?

Sure, you can attach the iSCSI disk yourself on the Dom0 and pass that
block device to the DomU, or you could even have a hotplug script that
does this automatically.

The nice thing from this implementation (apart from the fact that you
can specify iSCSI targets in the DomU config file, so you don't have to
care about plugging them), is that it allows to offload part of the work
that is usually done in the "add" phase to a new action called
"prepare", that when performing migration is executed before the guest
on the sender side is paused, so the blackout phase during migration is
reduced.

> 
> Completely untested, but if upstream QEMU device model is the 4.3
> default, upstream QEMU has its own native iscsi client built in.
> Won't that 'just work'? (with libxl, perhaps not xl)

Probably, but it will be much slower than blkback.


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