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RE: [Xen-API] RE: Questions about the api

To: Julian Chesterfield <Julian.Chesterfield@xxxxxxxxxxxxx>
Subject: RE: [Xen-API] RE: Questions about the api
From: Tomoiaga Cristian <cristi@xxxxxxxxxxx>
Date: Sat, 23 Oct 2010 12:20:06 +0300
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Thread-topic: [Xen-API] RE: Questions about the api
> Not sure I understand. You only need to export via iscsi when someone tries 
> to attach the snapshot or clone.


Yes, that's the way I do it right now, except for the snapshots. A snapshot 
can't be attached, don't really see a point right now, in XenServer you can 
only delete and clone a snap.
When you create a snapshot on my SR you will get a VDI that you can delete or 
clone just like in XenServer.
I've seen others (Netapp for example) creating a clone (double snapshot) when 
you vdi-snap or vdi-clone. An actual ZFS (and most likely Netapp) snapshot 
can't be exported unless you clone it.

>> Right now I am stuck with allowing all initiators in one pool to see 
>> all the luns in that pool.

>Hmm, that's a bit poor. 
>One approach is to hack the dom0 linux iscsi initiator to allow it to use 
>multiple initiator Ids at the same time (e.g. one per VM its performing IO 
>for). I think this is a relatively simple hack.
>Kinda like NPIV for iSCSI...

I am not sure if that solves the initial problem, except maybe if I create an 
initiator id for each lun, but that would be too much I believe. 
Currently I need a way to know the local disk path of a lun before I actually 
attach it and with the (currently missing) unique serial that would have been 
I will take a look at Nexenta, maybe I can add that functionality in the API 
especially since from the command line I can set a serial for a lun anytime.

>> Exclusion would have been good :(
>> Interested in that comparison also (with Comstar).

>Does the Solaris target support SCSI3 Persistent Reservations?

The default scsi implementation (not COMSTAR) does support SCSI3 PR, however 
that implementation is too slow to work with (missing writeback cache for 
The COMSTAR implementation also has support for it, at least in OpenSolaris 
(http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6795089). I will 
have to check on Nexenta.

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